glsl: fix bogus layout qualifier warnings
glsl: fix bogus layout qualifier warnings

Print out GL_ARB_explicit_attrib_location warnings only
when parsing attribute that uses "location" qualifier.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=77245
Signed-off-by: Tapani Pälli <cdcb67a5e49297de94340ca09f25994bd5e7f762@intel.com>
Reviewed-by: Anuj Phogat <e2026475996c48f0b97fd37e84129b3912980428@gmail.com>
Cc: "10.1 10.2" <59f39c0db42d4479a46b02d4d2bc11120e37bb44@lists.freedesktop.org>

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