This updates glslang to commit 9bb8cfffb0eed010e07132282c41d73064a7a609
which is the current version listed in the known_good.json file for the
version 1.3.212 of the Vulkan-ValidationLayers repo.
* -Wno-unused-but-set-variable: only set this flag with gcc, otherwise
clang will issue warnings about the warning option being unknown :)
(-Wunknown-warning-option)
* -Wmissing-variable-declarations: clang warns about missing extern
declarations for non-static variables.
iwubcode