firefox: add a patch to fix build.

srcpkgs/firefox/patches/shared-libs.patch

@@ -0,0 +1,11 @@
+--- browser/installer/Makefile.in	2012-07-17 16:19:29.480356991 +0000
++++ browser/installer/Makefile.in	2012-07-17 17:32:41.250937293 +0000
+@@ -50,7 +50,7 @@
+ MOZ_PKG_MANIFEST_P = $(srcdir)/package-manifest.in
+ # Some files have been already bundled with xulrunner
+ ifndef SYSTEM_LIBXUL
+-MOZ_PKG_FATAL_WARNINGS = 1
++MOZ_PKG_FATAL_WARNINGS = 0
+ endif
+
+ MOZ_NONLOCALIZED_PKG_LIST = \