gh-99942: fix regression in python.pc that broke linking on android/cygwin

In commit 254b309 a previous change to
avoid linking to libpython was partially reverted for Android (and later
Cygwin as well), to add back the link flags. This was applied to
distutils and to python-config.sh, but not to python.pc.

Add it back to python.pc as well.

Author: eli-schwartz

Misc/NEWS.d/next/Build/2022-12-20-01-06-17.gh-issue-99942.lbmzYj.rst

@@ -0,0 +1,2 @@
+On Android, python.pc now correctly reports the library to link to, the same
+as python-config.sh.

Misc/python.pc.in

@@ -9,5 +9,5 @@ Description: Build a C extension for Python
 Requires:
 Version: @VERSION@
 Libs.private: @LIBS@
-Libs:
+Libs: -L${libdir} @LIBPYTHON@
 Cflags: -I${includedir}/python@VERSION@@ABIFLAGS@