glsl: Write a new built-in function module.

glsl: Write a new built-in function module.

This creates a new replacement for the existing built-in function code.
The new module lives in builtin_functions.cpp (not builtin_function.cpp)
and exists in parallel with the existing system.  It isn't used yet.

The new built-in function code takes a significantly different approach:

Instead of implementing built-ins via printed IR, build time scripts,
and run time parsing, we now implement them directly in C++, using
ir_builder.  This translates to faster load times, and a much less
complex build system.

It also takes a different approach to built-in availability: each
signature now stores a boolean predicate, which makes it easy to
construct arbitrary expressions based on _mesa_glsl_parse_state's
fields.  This is much more flexible than the old system, and also
easier to use.

Built-ins are also now stored in a single gl_shader object, rather
than being spread out across a number of shaders that need to be linked.
When searching for a matching prototype, we simply consult the
availability predicate.  This also simplifies the code.

v2: Incorporate Matt Turner's feedback: use the new fma() function rather
    than expr().  Don't expose textureQueryLOD() in GLSL 4.00 (since it
    was renamed to textureQueryLod()).  Also correct some #undefs.
v3: Incorporate Paul Berry's feedback: rename legacy to compatibility;
    add comments to explain a few things; fix uvec availability; include
    shaderobj.h instead of repeating the _mesa_new_shader prototype.
v4: Fix lack of TEX_PROJECT on textureProjGrad[Offset] (caught by oglc).
    Add an out_var convenience function (more feedback by Matt Turner).
v5: Rework availability predicates for Lod functions.  They were broken.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Enthusiastically-acked-by: Paul Berry <stereotype441@gmail.com>