gcc: fix #12836: build on darwin

Patch is based on GCC Bug 66523:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66523

pkgs/development/compilers/gcc/4.9/default.nix

@@ -71,8 +71,10 @@ let version = "4.9.3";
       # The GNAT Makefiles did not pay attention to CFLAGS_FOR_TARGET for its
       # target libraries and tools.
       ++ optional langAda ../gnat-cflags.patch
-      ++ optional langFortran ../gfortran-driving.patch;
-
+      ++ optional langFortran ../gfortran-driving.patch
+      # The NXConstStr.patch can be removed at 4.9.4
+      ++ optional stdenv.isDarwin ../gfortran-darwin-NXConstStr.patch; 
+	  
     javaEcj = fetchurl {
       # The `$(top_srcdir)/ecj.jar' file is automatically picked up at
       # `configure' time.

pkgs/development/compilers/gcc/builder.sh

@@ -24,7 +24,7 @@ if test "$noSysDirs" = "1"; then
         # Figure out what extra flags to pass to the gcc compilers
         # being generated to make sure that they use our glibc.
         extraFlags="$(cat $NIX_CC/nix-support/libc-cflags)"
-        extraLDFlags="$(cat $NIX_CC/nix-support/libc-ldflags) $(cat $NIX_CC/nix-support/libc-ldflags-before)"
+        extraLDFlags="$(cat $NIX_CC/nix-support/libc-ldflags) $(cat $NIX_CC/nix-support/libc-ldflags-before || true)"
 
         # Use *real* header files, otherwise a limits.h is generated
         # that does not include Glibc's limits.h (notably missing

pkgs/development/compilers/gcc/gfortran-darwin-NXConstStr.patch

@@ -0,0 +1,27 @@
+From 82f81877458ea372176eabb5de36329431dce99b Mon Sep 17 00:00:00 2001
+From: Iain Sandoe <iain@codesourcery.com>
+Date: Sat, 21 Dec 2013 00:30:18 +0000
+Subject: [PATCH] don't try to mark local symbols as no-dead-strip
+
+---
+ gcc/config/darwin.c | 5 +++++
+ 1 file changed, 5 insertions(+)
+
+diff --git a/gcc/config/darwin.c b/gcc/config/darwin.c
+index 40804b8..0080299 100644
+--- a/gcc/config/darwin.c
++++ b/gcc/config/darwin.c
+@@ -1259,6 +1259,11 @@ darwin_encode_section_info (tree decl, rtx rtl, int first ATTRIBUTE_UNUSED)
+ void
+ darwin_mark_decl_preserved (const char *name)
+ {
++  /* Actually we shouldn't mark any local symbol this way, but for now
++     this only happens with ObjC meta-data.  */
++  if (darwin_label_is_anonymous_local_objc_name (name))
++    return;
++
+   fprintf (asm_out_file, "\t.no_dead_strip ");
+   assemble_name (asm_out_file, name);
+   fputc ('\n', asm_out_file);
+-- 
+2.2.1