gh-95855: Refactor platform triplet detection code, add detection for…

… MIPS soft float and musl libc (#107221)

- Move platform triplet detection code into Misc/platform_triplet.c
- Refactor MIPS detection, use defined(__mips64) to detect MIPS64
- Compute libc values in separate section
- Add detection for MIPS soft float
- Add detection for musl

musl supports SPE with its soft-float ABI:
https://git.musl-libc.org/cgit/musl/commit/?id=7be59733d71ada3a32a98622507399253f1d5e48

Original patch by Christian Heimes.

Co-authored-by: Christian Heimes <christian@python.org>
Co-authored-by: Erlend E. Aasland <erlend@python.org>

Misc/NEWS.d/next/Build/2023-07-25-02-30-00.gh-issue-95855.wA7rAf.rst

@@ -0,0 +1,2 @@
+Refactor platform triplet detection code and add detection for MIPS soft
+float and musl libc.

Misc/platform_triplet.c

@@ -0,0 +1,255 @@
+/* Detect platform triplet from builtin defines
+ * cc -E Misc/platform_triplet.c | grep '^PLATFORM_TRIPLET=' | tr -d ' '
+ */
+#undef bfin
+#undef cris
+#undef fr30
+#undef linux
+#undef hppa
+#undef hpux
+#undef i386
+#undef mips
+#undef powerpc
+#undef sparc
+#undef unix
+#if defined(__ANDROID__)
+    # Android is not a multiarch system.
+#elif defined(__linux__)
+/*
+ * BEGIN of Linux block
+ */
+// Detect libc (based on config.guess)
+# include <features.h>
+# if defined(__UCLIBC__)
+#  error uclibc not supported
+# elif defined(__dietlibc__)
+#  error dietlibc not supported
+# elif defined(__GLIBC__)
+#  define LIBC gnu
+#  define LIBC_X32 gnux32
+#  if defined(__ARM_PCS_VFP)
+#   define LIBC_ARM gnueabihf
+#  else
+#   define LIBC_ARM gnueabi
+#  endif
+#  if defined(__loongarch__)
+#   if defined(__loongarch_soft_float)
+#    define LIBC_LA gnusf
+#   elif defined(__loongarch_single_float)
+#    define LIBC_LA gnuf32
+#   elif defined(__loongarch_double_float)
+#    define LIBC_LA gnu
+#   else
+#    error unknown loongarch floating-point base abi
+#   endif
+#  endif
+#  if defined(_MIPS_SIM)
+#   if defined(__mips_hard_float)
+#    if _MIPS_SIM == _ABIO32
+#     define LIBC_MIPS gnu
+#    elif _MIPS_SIM == _ABIN32
+#     define LIBC_MIPS gnuabin32
+#    elif _MIPS_SIM == _ABI64
+#     define LIBC_MIPS gnuabi64
+#    else
+#     error unknown mips sim value
+#    endif
+#   else
+#    if _MIPS_SIM == _ABIO32
+#     define LIBC_MIPS gnusf
+#    elif _MIPS_SIM == _ABIN32
+#     define LIBC_MIPS gnuabin32sf
+#    elif _MIPS_SIM == _ABI64
+#     define LIBC_MIPS gnuabi64sf
+#    else
+#     error unknown mips sim value
+#    endif
+#   endif
+#  endif
+#  if defined(__SPE__)
+#   define LIBC_PPC gnuspe
+#  else
+#   define LIBC_PPC gnu
+#  endif
+# else
+// Heuristic to detect musl libc
+#  include <stdarg.h>
+#  ifdef __DEFINED_va_list
+#   define LIBC musl
+#   define LIBC_X32 muslx32
+#   if defined(__ARM_PCS_VFP)
+#    define LIBC_ARM musleabihf
+#   else
+#    define LIBC_ARM musleabi
+#   endif
+#   if defined(__loongarch__)
+#    if defined(__loongarch_soft_float)
+#     define LIBC_LA muslsf
+#    elif defined(__loongarch_single_float)
+#     define LIBC_LA muslf32
+#    elif defined(__loongarch_double_float)
+#     define LIBC_LA musl
+#    else
+#     error unknown loongarch floating-point base abi
+#    endif
+#   endif
+#   if defined(_MIPS_SIM)
+#    if defined(__mips_hard_float)
+#     if _MIPS_SIM == _ABIO32
+#      define LIBC_MIPS musl
+#     elif _MIPS_SIM == _ABIN32
+#      define LIBC_MIPS musln32
+#     elif _MIPS_SIM == _ABI64
+#      define LIBC_MIPS musl
+#     else
+#      error unknown mips sim value
+#     endif
+#    else
+#     if _MIPS_SIM == _ABIO32
+#      define LIBC_MIPS muslsf
+#     elif _MIPS_SIM == _ABIN32
+#      define LIBC_MIPS musln32sf
+#     elif _MIPS_SIM == _ABI64
+#      define LIBC_MIPS muslsf
+#     else
+#      error unknown mips sim value
+#     endif
+#    endif
+#   endif
+#   if defined(_SOFT_FLOAT) || defined(__NO_FPRS__)
+#    define LIBC_PPC muslsf
+#   else
+#    define LIBC_PPC musl
+#   endif
+#  else
+#   error unknown libc
+#  endif
+# endif
+
+# if defined(__x86_64__) && defined(__LP64__)
+PLATFORM_TRIPLET=x86_64-linux-LIBC
+# elif defined(__x86_64__) && defined(__ILP32__)
+PLATFORM_TRIPLET=x86_64-linux-LIBC_X32
+# elif defined(__i386__)
+PLATFORM_TRIPLET=i386-linux-LIBC
+# elif defined(__aarch64__) && defined(__AARCH64EL__)
+#  if defined(__ILP32__)
+PLATFORM_TRIPLET=aarch64_ilp32-linux-LIBC
+#  else
+PLATFORM_TRIPLET=aarch64-linux-LIBC
+#  endif
+# elif defined(__aarch64__) && defined(__AARCH64EB__)
+#  if defined(__ILP32__)
+PLATFORM_TRIPLET=aarch64_be_ilp32-linux-LIBC
+#  else
+PLATFORM_TRIPLET=aarch64_be-linux-LIBC
+#  endif
+# elif defined(__alpha__)
+PLATFORM_TRIPLET=alpha-linux-LIBC
+# elif defined(__ARM_EABI__)
+#  if defined(__ARMEL__)
+PLATFORM_TRIPLET=arm-linux-LIBC_ARM
+#  else
+PLATFORM_TRIPLET=armeb-linux-LIBC_ARM
+#  endif
+# elif defined(__hppa__)
+PLATFORM_TRIPLET=hppa-linux-LIBC
+# elif defined(__ia64__)
+PLATFORM_TRIPLET=ia64-linux-LIBC
+# elif defined(__loongarch__) && defined(__loongarch_lp64)
+PLATFORM_TRIPLET=loongarch64-linux-LIBC_LA
+# elif defined(__m68k__) && !defined(__mcoldfire__)
+PLATFORM_TRIPLET=m68k-linux-LIBC
+# elif defined(__mips__)
+#  if defined(__mips_isa_rev) && (__mips_isa_rev >=6)
+#   if defined(_MIPSEL) && defined(__mips64)
+PLATFORM_TRIPLET=mipsisa64r6el-linux-LIBC_MIPS
+#   elif defined(_MIPSEL)
+PLATFORM_TRIPLET=mipsisa32r6el-linux-LIBC_MIPS
+#   elif defined(__mips64)
+PLATFORM_TRIPLET=mipsisa64r6-linux-LIBC_MIPS
+#   else
+PLATFORM_TRIPLET=mipsisa32r6-linux-LIBC_MIPS
+#   endif
+#  else
+#   if defined(_MIPSEL) && defined(__mips64)
+PLATFORM_TRIPLET=mips64el-linux-LIBC_MIPS
+#   elif defined(_MIPSEL)
+PLATFORM_TRIPLET=mipsel-linux-LIBC_MIPS
+#   elif defined(__mips64)
+PLATFORM_TRIPLET=mips64-linux-LIBC_MIPS
+#   else
+PLATFORM_TRIPLET=mips-linux-LIBC_MIPS
+#   endif
+#  endif
+# elif defined(__or1k__)
+PLATFORM_TRIPLET=or1k-linux-LIBC
+# elif defined(__powerpc64__)
+#  if defined(__LITTLE_ENDIAN__)
+PLATFORM_TRIPLET=powerpc64le-linux-LIBC
+#  else
+PLATFORM_TRIPLET=powerpc64-linux-LIBC
+#  endif
+# elif defined(__powerpc__)
+PLATFORM_TRIPLET=powerpc-linux-LIBC_PPC
+# elif defined(__s390x__)
+PLATFORM_TRIPLET=s390x-linux-LIBC
+# elif defined(__s390__)
+PLATFORM_TRIPLET=s390-linux-LIBC
+# elif defined(__sh__) && defined(__LITTLE_ENDIAN__)
+PLATFORM_TRIPLET=sh4-linux-LIBC
+# elif defined(__sparc__) && defined(__arch64__)
+PLATFORM_TRIPLET=sparc64-linux-LIBC
+# elif defined(__sparc__)
+PLATFORM_TRIPLET=sparc-linux-LIBC
+# elif defined(__riscv)
+#  if __riscv_xlen == 32
+PLATFORM_TRIPLET=riscv32-linux-LIBC
+#  elif __riscv_xlen == 64
+PLATFORM_TRIPLET=riscv64-linux-LIBC
+#  else
+#   error unknown platform triplet
+#  endif
+# else
+#   error unknown platform triplet
+# endif
+/*
+ * END of Linux block
+ */
+#elif defined(__FreeBSD_kernel__)
+# if defined(__LP64__)
+PLATFORM_TRIPLET=x86_64-kfreebsd-gnu
+# elif defined(__i386__)
+PLATFORM_TRIPLET=i386-kfreebsd-gnu
+# else
+#   error unknown platform triplet
+# endif
+#elif defined(__gnu_hurd__)
+PLATFORM_TRIPLET=i386-gnu
+#elif defined(__APPLE__)
+PLATFORM_TRIPLET=darwin
+#elif defined(__VXWORKS__)
+PLATFORM_TRIPLET=vxworks
+#elif defined(__wasm32__)
+#  if defined(__EMSCRIPTEN__)
+PLATFORM_TRIPLET=wasm32-emscripten
+#  elif defined(__wasi__)
+#    if defined(_REENTRANT)
+PLATFORM_TRIPLET=wasm32-wasi-threads
+#    else
+PLATFORM_TRIPLET=wasm32-wasi
+#    endif
+#  else
+#    error unknown wasm32 platform
+#  endif
+#elif defined(__wasm64__)
+#  if defined(__EMSCRIPTEN__)
+PLATFORM_TRIPLET=wasm64-emscripten
+#  elif defined(__wasi__)
+PLATFORM_TRIPLET=wasm64-wasi
+#  else
+#    error unknown wasm64 platform
+#  endif
+#else
+# error unknown platform triplet
+#endif