mesa: Introduce a compiler enum for tessellation spacing.

It feels weird using GL_* enums in a Vulkan driver.

v2: Fix the TESS_SPACING -> PIPE_TESS_SPACING conversion.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/compiler/glsl/ast.h

@@ -704,7 +704,7 @@ struct ast_type_qualifier {
    ast_layout_expression *local_size[3];
 
    /** Tessellation evaluation shader: vertex spacing (equal, fractional even/odd) */
-   GLenum vertex_spacing;
+   enum gl_tess_spacing vertex_spacing;
 
    /** Tessellation evaluation shader: vertex ordering (CW or CCW) */
    GLenum ordering;