glsl/glcpp: Treat carriage return as equivalent to line feed.

glsl/glcpp: Treat carriage return as equivalent to line feed.

Previously, the '\r' character was not explicitly matched by any lexer
rule. This means that glcpp would have been using the default flex rule to
match '\r' characters, (where they would have been printed to stdout rather
than actually correctly handled).

With this commit, we treat '\r' as equivalent to '\n'. This is clearly an
improvement the bogus printing to stdout. The resulting behavior is compliant
with the GLSL specification for any source file that uses exclusively '\r' or
'\n' to separate lines.

For shaders that use a multiple-character line separator, (such as "\r\n"),
glcpp won't be precisely compliant with the specification, (treating these as
two newline characters rather than one), but this should not introduce any
semantic changes to the shader programs.

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