glsl/glcpp: Rename HASH token to HASH_TOKEN

glsl/glcpp: Rename HASH token to HASH_TOKEN

This is in preparation for the planned addition of a new <HASH> start
condition to the lexer. Both start conditions and token types are, of course,
in the same default C namespace, so a start condition and a token type with
the same name will collide. (And unfortunately, they are both apparently
implemented as equivalent numeric types so the collision is undetected at
compile time and simply leads to unpredictable behavior at run time.)

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>