Save about 100K.
N.B.: This is done by eliminating a function call, at a high level,
not by #ifdef'ing a bunch of code.
Also, removed no longer needed *_EXTENSION #ifdef in the code not
needed by GLSLANG_WEB.
One variable was only used in an 'assert' call. MSVC flagged this
as unused in Release. Suppress the warning and also add a static
cast to void so the variable becomes referenced.
Last year we changed 'volatile' to also act as 'coherent', but when I
resolved the memory model changes against that change I missed handling
volatile in a couple places that we check for coherent. There was also
a place in post-processing that acted as if the volatile memory access
flag has a literal number associated with it, when it doesn't.
When capabilities are needed for specific SPIR-V instructions, it is
fragile to do so based on GLSL/AST usage; it should be based on actual
instructions they got translated to.
