Contribs: apply OSX patch only on OSX

Else, it conflicts with Win32 patch and fails to compile

(cherry picked from commit f836a94d9c4a78a03cc412d5559d274dc2df459b)
Signed-off-by: Rafaël Carré <funman@videolan.org>

contrib/src/gnutls/rules.mak

@@ -28,7 +28,9 @@ endif
 	$(APPLY) $(SRC)/gnutls/gnutls-no-egd.patch
 	$(APPLY) $(SRC)/gnutls/read-file-limits.h.patch
 	$(APPLY) $(SRC)/gnutls/mac-keychain-lookup.patch
+ifdef HAVE_MACOSX
 	$(APPLY) $(SRC)/gnutls/gnutls-pkgconfig-osx.patch
+endif
 	$(call pkg_static,"lib/gnutls.pc.in")
 	$(UPDATE_AUTOCONFIG)
 	$(MOVE)