DEBUG: CI: compilation-checks.yml add empty arch_ext

Signed-Off-By: Michael Cobb (The Capable Hub) <mcobb@thegoodpenguin.co.uk>

Author: michaelcobb-capablehub

.github/workflows/compilation-checks.yml

@@ -30,6 +30,7 @@ jobs:
         # RISCV32 and IA32 are left out, as they have no verified config
         arch: [ARM, ARM_HYP, AARCH64, RISCV64, X64]
         compiler: [gcc, llvm]
+        arch_ext: [""]
         include:
           - arch: RISCV64
             compiler: llvm