toolchain: Update to glslang 31490 and LunarGLASS 1091

Also contains commits:

Author: GregF <greg@LunarG.com>
Date:   Thu May 28 09:30:14 2015 -0600

    compiler: handle new builtIn enum in metadata

Author: Cody Northrop <cody@lunarg.com>
Date:   Mon Jun 1 14:24:26 2015 -0600

    compiler: Update backend for new sampler types and switches
diff --git a/update_external_sources.sh b/update_external_sources.sh
index efeafe4..7beb68a 100755
--- a/update_external_sources.sh
+++ b/update_external_sources.sh
@@ -1,8 +1,8 @@
 #!/bin/bash
 # Update source for glslang and LLVM
 
-LUNARGLASS_REVISION=1070
-GLSLANG_REVISION=30939
+LUNARGLASS_REVISION=1091
+GLSLANG_REVISION=31490
 
 BUILDDIR=$PWD
 BASEDIR=$BUILDDIR/..