glsl/glcpp: Add testing for EOF sans newline (and fix for <DEFINE>, <COMMENT>)

glsl/glcpp: Add testing for EOF sans newline (and fix for <DEFINE>, <COMMENT>)

The glcpp implementation has long had code to support a file that ends without
a final newline. But we didn't have a "make check" test for this.

Additionally, the <EOF> action was restricted only to the <INITIAL> state so
it would fail to get invoked if the EOF was encountered in the <COMMENT> or
the <DEFINE> case. Neither of these was a bug, per se, since EOF in either
of these cases is an error anyway, (either "unterminated comment" or
"missing macro name for #define").

But with the new explicit support for these cases, we not generate clean error
messages in these cases, (rather than "unexpected $end" from before).

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