gh-99942: correct the pkg-config/python-config flags for cygwin/android

On shared build configurations, Cygwin and Android need to link to
libpython. See bpo-21536.

This was corrected in distutils with an explicit check to only link when
libpython is built shared, but implemented in configure.ac
unconditionally. The correct approach is to follow distutils, which
includes a comment regarding why:

- on Android, a shared libpython is RTLD_LOCAL, and thus available only
  to the main executable, not exported to loaded modules, but a static
  libpython *is* the main executable and thus exported

- on Cygwin, symbols in shared libraries must be resolved at link time

It's actually not clear to me what to do for Cygwin. Cygwin doesn't
actually build static libpython successfully. If it did, then extensions
probably need to be linked to the import library for the executable,
rather than the full static library. So omitting this here is probably
correct, but incomplete. Either way, it won't matter until other fixes
are made.

Misc/NEWS.d/next/Build/2023-01-12-00-49-16.gh-issue-99942.DUR8b4.rst

@@ -0,0 +1,2 @@
+On Android, in a static build, python-config in embed mode no longer
+incorrectly reports a library to link to.

configure.ac

@@ -5830,7 +5830,7 @@ AC_MSG_RESULT($LDVERSION)
 
 # On Android and Cygwin the shared libraries must be linked with libpython.
 AC_SUBST(LIBPYTHON)
-if test -n "$ANDROID_API_LEVEL" -o "$MACHDEP" = "cygwin"; then
+if test "$PY_ENABLE_SHARED" = "1" && ( test -n "$ANDROID_API_LEVEL" || test "$MACHDEP" = "cygwin"); then
   LIBPYTHON="-lpython${VERSION}${ABIFLAGS}"
 else
   LIBPYTHON=''