GH-138800: fix variable substitution in python3.pc for Android

Makefile.pre.in

@@ -285,6 +285,7 @@ DIST=		$(DISTFILES) $(DISTDIRS)
 LIBRARY=	@LIBRARY@
 LDLIBRARY=      @LDLIBRARY@
 BLDLIBRARY=     @BLDLIBRARY@
+MODULE_LDFLAGS_SHARED=$(if $(LIBPYTHON),$(BLDLIBRARY))
 PY3LIBRARY=     @PY3LIBRARY@
 DLLLIBRARY=	@DLLLIBRARY@
 LDLIBRARYDIR=   @LDLIBRARYDIR@

Misc/NEWS.d/next/Build/2026-03-07-02-09-57.gh-issue-138800.VD8qbz.rst

@@ -0,0 +1 @@
+Fix library name in python3.pc on Android.

Modules/makesetup

@@ -277,7 +277,7 @@ sed -e 's/[ 	]*#.*//' -e '/^[ 	]*$/d' |
 				;;
 			esac
 			rule="$file: $objs \$(MODULE_${mods_upper}_LDEPS)"
-			rule="$rule; \$(BLDSHARED) $objs $libs \$(LIBPYTHON) -o $file"
+			rule="$rule; \$(BLDSHARED) $objs $libs \$(MODULE_LDFLAGS_SHARED) -o $file"
 			echo "$rule" >>$rulesf
 		done
 	done

configure.ac

@@ -6669,18 +6669,21 @@ LDVERSION='$(VERSION)$(ABIFLAGS)'
 AC_MSG_RESULT([$LDVERSION])
 
 # Configure the flags and dependencies used when compiling shared modules.
-# Do not rename LIBPYTHON - it's accessed via sysconfig by package build
-# systems (e.g. Meson) to decide whether to link extension modules against
-# libpython.
 AC_SUBST([MODULE_DEPS_SHARED])
 AC_SUBST([LIBPYTHON])
 MODULE_DEPS_SHARED='$(MODULE_DEPS_STATIC) $(EXPORTSYMS)'
+
+# On most platforms, extension modules aren't linked against libpython, so
+# LIBPYTHON must be empty.
 LIBPYTHON=''
 
 # On Android and Cygwin the shared libraries must be linked with libpython.
+# LIBPYTHON is used by python-config, python3.pc, the commands for building the
+# stdlib's own extension modules, and external package build systems via
+# sysconfig, so its value must be suitable for all those contexts.
 if test "$PY_ENABLE_SHARED" = "1" && ( test -n "$ANDROID_API_LEVEL" || test "$MACHDEP" = "cygwin"); then
   MODULE_DEPS_SHARED="$MODULE_DEPS_SHARED \$(LDLIBRARY)"
-  LIBPYTHON="\$(BLDLIBRARY)"
+  LIBPYTHON="-lpython${VERSION}${ABIFLAGS}"
 fi
 
 # On iOS the shared libraries must be linked with the Python framework