spirv: Handle instruction aliases in vtn_gather_types

Same solution as done in spirv_info generation.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4682>

src/compiler/spirv/vtn_gather_types_c.py

@@ -29,7 +29,13 @@ from sys import stdout
 from mako.template import Template
 
 def find_result_types(spirv):
+    seen = set()
     for inst in spirv['instructions']:
+        # Handle aliases by choosing the first one in the grammar.
+        if inst['opcode'] in seen:
+            continue
+        seen.add(inst['opcode'])
+
         name = inst['opname']
 
         if 'operands' not in inst: