mesa/compiler: add stage to shader_info

This will allow us to simplify the current program logic for SSO.

Also since we aim to detach shader_info from nir_shader this will come
in handy avoiding passing nir_shader around just to keep track of
the stage we are dealing with.

V2: set stage for arb asm programs also.

Reviewed-by: Eric Anholt <eric@anholt.net>

src/compiler/shader_info.h

@@ -32,6 +32,9 @@ extern "C" {
 #endif
 
 typedef struct shader_info {
+   /** The shader stage, such as MESA_SHADER_VERTEX. */
+   gl_shader_stage stage;
+
    const char *name;
 
    /* Descriptive name provided by the client; may be NULL */