toolchain: Update to latest glslang and LunarGLASS, fix script

glslang hash: e6f7988adec197e0590fb8274b0412811456d3e6
LunarGLASS revision: 1093

Also, ensure update_external_sources.* fetches the repo before
checking out the hash.
diff --git a/glslang_revision b/glslang_revision
index 33b51a0..565eaa4 100644
--- a/glslang_revision
+++ b/glslang_revision
@@ -1 +1 @@
-9e41f362a6ee3118b61f076ee156125b59b3a005
+e6f7988adec197e0590fb8274b0412811456d3e6