widl: Make constdef and externdef take a declarator instead of an ident so that functions and arrays can be defined using the statements.

Fix applying calling convention to function type.

Use an attribute to store the const qualifier for the pointer and type.

Allow multiple type-qualifiers to be applied to a type by adding a 
declaration-specifier rule that encompasses type-qualifiers and types.

wgl: We were already advertising GL_EXT_framebuffer_sRGB but not the corresponding WGL_FRAMEBUFFER_SRGB_CAPABLE_EXT.