gfxstream: mark unused variables as such

It's unclear to me whether this is dead code that should be removed or
dead code that should be used, so I just marked it as unused to remove
a few thousand warnings when compiling.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33384>

src/gfxstream/codegen/scripts/cereal/counting.py

@@ -78,6 +78,7 @@ class VulkanCountingCodegen(VulkanTypeIterator):
                 makeVulkanTypeSimple(False, "uint64_t", 1, paramName=handle64Var)
         else:
             self.cgen.stmt("uint64_t %s" % handle64Var)
+            self.cgen.stmt("(void)%s" % handle64Var)
             handle64VarAccess = "&%s" % handle64Var
             handle64VarType = \
                 makeVulkanTypeSimple(False, "uint64_t", 0, paramName=handle64Var)

src/gfxstream/codegen/scripts/cereal/marshaling.py

@@ -195,6 +195,7 @@ class VulkanMarshalingCodegen(VulkanTypeIterator):
             checkName = "check_%s" % vulkanType.paramName
             self.cgen.stmt("%s %s" % (
                 self.cgen.makeCTypeDecl(vulkanType, useParamName = False), checkName))
+            self.cgen.stmt("(void)%s" % checkName)
             checkAccess = checkName
             addrExpr = "&" + checkAccess
             sizeExpr = self.cgen.sizeofExpr(vulkanType)