glcpp: Add support for __LINE__ and __FILE__ macros

glcpp: Add support for __LINE__ and __FILE__ macros

These tokens are easy to expand by just looking at the current, tracked
location values, (and no need to look anything up in the hash table).

Add a test which verifies __LINE__ with several values, (and verifies __FILE__
for the single value of 0). Our testing framework isn't sophisticated enough
here to have a test with multiple file inputs.

This commit fixes part of es3conform's preprocess16_frag test.

Reviewed-by: Matt Turner <mattst88@gmail.com>