contrib: gme: Prepare pkgconfig file and list lc++ on mac

On mac, we use libc++ instead of libstdc++. While the library is
actually build against libc++ already, the pkgconfig file still
hardcoded libstdc++ instead.

Refs #27262

contrib/src/gme/mac-use-c-stdlib.patch

+--- game-music-emu/gme/libgme.pc.in.old	2022-08-25 21:46:36.000000000 +0200
++++ game-music-emu/gme/libgme.pc.in	2022-08-25 21:46:57.000000000 +0200
+@@ -13,4 +13,4 @@
+ Version: @GME_VERSION@
+ Cflags: -I${includedir}
+ Libs: -L${libdir} -lgme
+-Libs.private: -lstdc++ -lm @PKG_CONFIG_ZLIB@
++Libs.private: -lc++ -lm @PKG_CONFIG_ZLIB@

contrib/src/gme/rules.mak

@@ -16,6 +16,9 @@ game-music-emu: game-music-emu-$(GME_VERSION).tar.xz .sum-gme
 	$(UNPACK)
 	$(APPLY) $(SRC)/gme/skip-underrun.patch
 	$(APPLY) $(SRC)/gme/add-libm.patch
+ifdef HAVE_MACOSX
+	$(APPLY) $(SRC)/gme/mac-use-c-stdlib.patch
+endif
 	$(call pkg_static,"gme/libgme.pc.in")
 	$(MOVE)