Unify how platforms are detected in toolchain file

eng/common/cross/toolchain.cmake

@@ -3,18 +3,26 @@ set(CROSS_ROOTFS $ENV{ROOTFS_DIR})
 set(TARGET_ARCH_NAME $ENV{TARGET_BUILD_ARCH})
 if(EXISTS ${CROSS_ROOTFS}/bin/freebsd-version)
   set(CMAKE_SYSTEM_NAME FreeBSD)
+  set(FREEBSD 1)
 elseif(EXISTS ${CROSS_ROOTFS}/usr/platform/i86pc)
   set(CMAKE_SYSTEM_NAME SunOS)
   set(ILLUMOS 1)
 else()
   set(CMAKE_SYSTEM_NAME Linux)
+  set(LINUX 1)
 endif()
 set(CMAKE_SYSTEM_VERSION 1)
 
+if(EXISTS ${CROSS_ROOTFS}/etc/tizen-release)
+  set(TIZEN 1)
+elseif(EXISTS ${CROSS_ROOTFS}/android_platform)
+  set(ANDROID 1)
+endif()
+
 if(TARGET_ARCH_NAME STREQUAL "armel")
   set(CMAKE_SYSTEM_PROCESSOR armv7l)
   set(TOOLCHAIN "arm-linux-gnueabi")
-  if("$ENV{__DistroRid}" MATCHES "tizen.*")
+  if(TIZEN)
     set(TIZEN_TOOLCHAIN "armv7l-tizen-linux-gnueabi/9.2.0")
   endif()
 elseif(TARGET_ARCH_NAME STREQUAL "arm")
@@ -26,7 +34,7 @@ elseif(TARGET_ARCH_NAME STREQUAL "arm")
   else()
     set(TOOLCHAIN "arm-linux-gnueabihf")
   endif()
-  if("$ENV{__DistroRid}" MATCHES "tizen.*")
+  if(TIZEN)
     set(TIZEN_TOOLCHAIN "armv7hl-tizen-linux-gnueabihf/9.2.0")
   endif()
 elseif(TARGET_ARCH_NAME STREQUAL "arm64")
@@ -36,7 +44,7 @@ elseif(TARGET_ARCH_NAME STREQUAL "arm64")
   else()
     set(TOOLCHAIN "aarch64-linux-gnu")
   endif()
-  if("$ENV{__DistroRid}" MATCHES "tizen.*")
+  if(TIZEN)
     set(TIZEN_TOOLCHAIN "aarch64-tizen-linux-gnu/9.2.0")
   endif()
 elseif(TARGET_ARCH_NAME STREQUAL "s390x")
@@ -45,7 +53,7 @@ elseif(TARGET_ARCH_NAME STREQUAL "s390x")
 elseif(TARGET_ARCH_NAME STREQUAL "x86")
   set(CMAKE_SYSTEM_PROCESSOR i686)
   set(TOOLCHAIN "i686-linux-gnu")
-elseif (CMAKE_SYSTEM_NAME STREQUAL "FreeBSD")
+elseif (FREEBSD)
   set(CMAKE_SYSTEM_PROCESSOR "x86_64")
   set(triple "x86_64-unknown-freebsd12")
 elseif (ILLUMOS)
@@ -60,7 +68,7 @@ if(DEFINED ENV{TOOLCHAIN})
 endif()
 
 # Specify include paths
-if(DEFINED TIZEN_TOOLCHAIN)
+if(TIZEN)
   if(TARGET_ARCH_NAME STREQUAL "arm")
     include_directories(SYSTEM ${CROSS_ROOTFS}/usr/lib/gcc/${TIZEN_TOOLCHAIN}/include/c++/)
     include_directories(SYSTEM ${CROSS_ROOTFS}/usr/lib/gcc/${TIZEN_TOOLCHAIN}/include/c++/armv7hl-tizen-linux-gnueabihf)
@@ -75,15 +83,17 @@ if(DEFINED TIZEN_TOOLCHAIN)
   endif()
 endif()
 
-if("$ENV{__DistroRid}" MATCHES "android.*")
+if(ANDROID)
     if(TARGET_ARCH_NAME STREQUAL "arm")
         set(ANDROID_ABI armeabi-v7a)
     elseif(TARGET_ARCH_NAME STREQUAL "arm64")
         set(ANDROID_ABI arm64-v8a)
     endif()
 
     # extract platform number required by the NDK's toolchain
-    string(REGEX REPLACE ".*\\.([0-9]+)-.*" "\\1" ANDROID_PLATFORM "$ENV{__DistroRid}")
+    file(READ "${CROSS_ROOTFS}/android_platform" RID_FILE_CONTENTS)
+    string(REPLACE "RID=" "" ANDROID_RID "${RID_FILE_CONTENTS}")
+    string(REGEX REPLACE ".*\\.([0-9]+)-.*" "\\1" ANDROID_PLATFORM "${ANDROID_RID}")
 
     set(ANDROID_TOOLCHAIN clang)
     set(FEATURE_EVENT_TRACE 0) # disable event trace as there is no lttng-ust package in termux repository
@@ -92,7 +102,7 @@ if("$ENV{__DistroRid}" MATCHES "android.*")
 
     # include official NDK toolchain script
     include(${CROSS_ROOTFS}/../build/cmake/android.toolchain.cmake)
-elseif(CMAKE_SYSTEM_NAME STREQUAL "FreeBSD")
+elseif(FREEBSD)
     # we cross-compile by instructing clang
     set(CMAKE_C_COMPILER_TARGET ${triple})
     set(CMAKE_CXX_COMPILER_TARGET ${triple})
@@ -152,20 +162,20 @@ function(add_toolchain_linker_flag Flag)
   set("CMAKE_SHARED_LINKER_FLAGS${CONFIG_SUFFIX}_INIT" "${CMAKE_SHARED_LINKER_FLAGS${CONFIG_SUFFIX}_INIT} ${Flag}" PARENT_SCOPE)
 endfunction()
 
-if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
+if(LINUX)
   add_toolchain_linker_flag("-Wl,--rpath-link=${CROSS_ROOTFS}/lib/${TOOLCHAIN}")
   add_toolchain_linker_flag("-Wl,--rpath-link=${CROSS_ROOTFS}/usr/lib/${TOOLCHAIN}")
 endif()
 
-if(TARGET_ARCH_NAME STREQUAL "arm" OR TARGET_ARCH_NAME STREQUAL "armel")
-  if(DEFINED TIZEN_TOOLCHAIN) # For Tizen only
+if(TARGET_ARCH_NAME MATCHES "^(arm|armel)$")
+  if(TIZEN)
     add_toolchain_linker_flag("-B${CROSS_ROOTFS}/usr/lib/gcc/${TIZEN_TOOLCHAIN}")
     add_toolchain_linker_flag("-L${CROSS_ROOTFS}/lib")
     add_toolchain_linker_flag("-L${CROSS_ROOTFS}/usr/lib")
     add_toolchain_linker_flag("-L${CROSS_ROOTFS}/usr/lib/gcc/${TIZEN_TOOLCHAIN}")
   endif()
 elseif(TARGET_ARCH_NAME STREQUAL "arm64")
-  if(DEFINED TIZEN_TOOLCHAIN) # For Tizen only
+  if(TIZEN)
     add_toolchain_linker_flag("-B${CROSS_ROOTFS}/usr/lib64/gcc/${TIZEN_TOOLCHAIN}")
     add_toolchain_linker_flag("-L${CROSS_ROOTFS}/lib64")
     add_toolchain_linker_flag("-L${CROSS_ROOTFS}/usr/lib64")
@@ -184,7 +194,7 @@ endif()
 
 # Specify compile options
 
-if((TARGET_ARCH_NAME MATCHES "^(arm|armel|arm64|s390x)$" AND NOT "$ENV{__DistroRid}" MATCHES "android.*") OR ILLUMOS)
+if((TARGET_ARCH_NAME MATCHES "^(arm|armel|arm64|s390x)$" AND NOT ANDROID) OR ILLUMOS)
   set(CMAKE_C_COMPILER_TARGET ${TOOLCHAIN})
   set(CMAKE_CXX_COMPILER_TARGET ${TOOLCHAIN})
   set(CMAKE_ASM_COMPILER_TARGET ${TOOLCHAIN})
@@ -211,7 +221,7 @@ elseif(TARGET_ARCH_NAME STREQUAL "x86")
   add_compile_options(-Wno-error=unused-command-line-argument)
 endif()
 
-if(DEFINED TIZEN_TOOLCHAIN)
+if(TIZEN)
   if(TARGET_ARCH_NAME MATCHES "^(arm|armel|arm64)$")
     add_compile_options(-Wno-deprecated-declarations) # compile-time option
     add_compile_options(-D__extern_always_inline=inline) # compile-time option