Bug 1029245 - part 1 - modify build-gcc.sh to build GCC 4.9.4; r=glandium

PR 64905 apparently never got backported to 4.9.x, so we still need the
patch for that.

build/unix/build-gcc/build-gcc.sh

@@ -1,6 +1,6 @@
 #!/bin/bash
 
-gcc_version=4.8.5
+gcc_version=4.9.4
 binutils_version=2.25.1
 this_path=$(readlink -f $(dirname $0))
 make_flags='-j12'