glsl: Take advantage of the layout qualifier flags union to clean up parsing.

glsl: Take advantage of the layout qualifier flags union to clean up parsing.

The got_one variable was set iff one of the bits in flags.i was set.

v2: Fix incorrect dropping of the ARB_conservative_depth warning.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org> (v1)
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>