glsl: A shader cannot redefine or overload built-in functions in GLSL ES 3.00

glsl: A shader cannot redefine or overload built-in functions in GLSL ES 3.00

Create a new search function to look for matching built-in functions by name
and use it for built-in function redefinition or overload in GLSL ES 3.00.

GLSL ES 3.0 spec, chapter 6.1 "Function Definitions", page 71

  "A shader cannot redefine or overload built-in functions."

While in GLSL ES 1.0 specification, chapter 8 "Built-in Functions"

  "User code can overload the built-in functions but cannot redefine them."

So this check is specific to GLSL ES 3.00.

This patch fixes the following dEQP tests:

dEQP-GLES3.functional.shaders.functions.invalid.overload_builtin_function_vertex
dEQP-GLES3.functional.shaders.functions.invalid.overload_builtin_function_fragment
dEQP-GLES3.functional.shaders.functions.invalid.redefine_builtin_function_vertex
dEQP-GLES3.functional.shaders.functions.invalid.redefine_builtin_function_fragment

No piglit regressions.

Signed-off-by: Samuel Iglesias Gonsalvez <siglesias@igalia.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>