glsl/glcpp: Emit error for duplicate parameter name in function-like macro

This will emit an error for something like:

	#define FOO(x,x) ...

Obviously, it's not a legal thing to do, and it's easy to check.

Add a "make check" test for this as well.

This fixes the following Khronos GLES3 CTS tests:

	invalid_function_definitions.unique_param_name_vertex
	invalid_function_definitions.unique_param_name_fragment

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

src/glsl/glcpp/tests/135-duplicate-parameter.c

@@ -0,0 +1,2 @@
+#define FOO(a,a) which a?
+#define BAR(x,y,z,x) so very x

src/glsl/glcpp/tests/135-duplicate-parameter.c.expected

@@ -0,0 +1,4 @@
+0:1(9): preprocessor error: Duplicate macro parameter "a"
+0:2(9): preprocessor error: Duplicate macro parameter "x"
+
+