glsl: Reallow precision qualifiers on structure members

glsl: Reallow precision qualifiers on structure members

Changes to the grammar for GL_ARB_shading_language_420pack (commit
6eec502) moved precision qualifiers out of the type_specifier production
chain.  This caused declarations such as:

    struct S {
        lowp float f;
    };

to generate parse errors.  Section 4.1.8 (Structures) of both the GLSL
ES 1.00 spec and GLSL 1.30 specs says:

        "Member declarators may contain precision qualifiers, but may not
        contain any other qualifiers."

So, it sure seems like we shouldn't generate a parse error. :)

Instead of type_specifier, use fully_specified_type in struct members.
However, fully_specified_type allows a lot of other qualifiers that are
not allowed on structure members, so expeclitly disallow them.

Note, this makes struct_declaration look an awful lot like
member_declaration (used for interface blocks).  We may want to
(somehow) unify these rules to reduce code duplication at some point.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=68753
Reported-by: Aras Pranckevicius <aras@unity3d.com>
Cc: Aras Pranckevicius <aras@unity3d.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Cc: "9.2" <mesa-stable@lists.freedesktop.org>