glsl: Add an internal-error catch-all rule

glsl: Add an internal-error catch-all rule

This is to avoid the default, silent flex rule which simply prints the
character to stdout.

For the following Khronos GLES3 conformance tests:

	invalid_char_in_name_vertex
	invalid_char_in_name_fragment

With this commit, these tests now report Pass where they previously reported
Fail, but Mesa isn't behaving correctly yet. It's now reporting the internal
error where what is really desired is a syntax error.

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