mesa/compiler: move MAX_VARYING to shader_enums.h

Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>

src/compiler/shader_enums.h

@@ -172,6 +172,7 @@ const char *gl_vert_attrib_name(gl_vert_attrib attrib);
    BITFIELD64_RANGE(VERT_ATTRIB_GENERIC(0), VERT_ATTRIB_GENERIC_MAX)
 /*@}*/
 
+#define MAX_VARYING 32 /**< number of float[4] vectors */
 
 /**
  * Indexes for vertex shader outputs, geometry shader inputs/outputs, and