glsl: fixer lexer for unreachable defines

If we have something like:

   #ifdef NOT_DEFINED
   #define A_MACRO(x) \
	if (x)
   #endif

The # on the #define is not skipped but the define itself is so
this then gets recognised as #if.

Until 28a3731e this didn't happen because we ended up in
<HASH>{NONSPACE} where BEGIN INITIAL was called stopping the
problem from happening.

This change makes sure we never call RETURN_TOKEN_NEVER_SKIP for
if/else/endif when processing a define.

Cc: Ian Romanick <idr@freedesktop.org>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107772