glsl/types: Expose the function_param and struct_field structs to C
glsl/types: Expose the function_param and struct_field structs to C

Previously, they were hidden behind a #ifdef __cplusplus so C wouldn't find
them.  This commit simpliy moves the #ifdef and adds #ifdef's around
constructors.

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler