Bug 1175359 - Enable rust in linux64 builds. r=ted

Write a mozconfig fragment which makes the rust toolchain
provided by tooltool available for linux builds.

Use linux64 mozconfigs to enable rust for official builds of
that target. These aren't used outside of automation builds,
so including rust there will verify code on check-in without
requiring developers to install rust.

browser/config/mozconfigs/linux64/beta

@@ -4,4 +4,6 @@ ac_add_options --enable-official-branding
 
 mk_add_options MOZ_PGO=1
 
+. "$topsrcdir/build/unix/mozconfig.rust.linux"
+
 . "$topsrcdir/build/mozconfig.common.override"

browser/config/mozconfigs/linux64/debug

@@ -21,4 +21,6 @@ export MOZ_PACKAGE_JSSHELL=1
 
 ac_add_options --with-branding=browser/branding/nightly
 
+. "$topsrcdir/build/unix/mozconfig.rust.linux"
+
 . "$topsrcdir/build/mozconfig.common.override"

browser/config/mozconfigs/linux64/nightly

@@ -16,4 +16,6 @@ ac_add_options --with-branding=browser/branding/nightly
 # Use ccache
 . "$topsrcdir/build/mozconfig.cache"
 
+. "$topsrcdir/build/unix/mozconfig.rust.linux"
+
 . "$topsrcdir/build/mozconfig.common.override"

browser/config/mozconfigs/linux64/release

@@ -10,4 +10,6 @@ mk_add_options MOZ_PGO=1
 # defines.sh during the beta cycle
 export BUILDING_RELEASE=1
 
+. "$topsrcdir/build/unix/mozconfig.rust.linux"
+
 . "$topsrcdir/build/mozconfig.common.override"

build/unix/mozconfig.rust.linux

@@ -0,0 +1,5 @@
+# Options to enable rust in automation builds.
+
+RUSTC="$topsrcdir/rustc/bin/rustc"
+mk_add_options "export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:$topsrcdir/rustc/lib"
+ac_add_options --enable-rust