CI: re-add RISCV64, then exclude it

Signed-Off-By: Michael Cobb <michael.cobb@thecapablehub.org>

Author: michaelcobb-capablehub

.github/workflows/compilation-checks.yml

@@ -30,8 +30,10 @@ jobs:
       matrix:
         # RISCV32 and IA32 are left out, as they have no verified config
         #arch: [ARM, ARM_HYP, AARCH64, RISCV64, X64]
-        arch: [ ]
+        arch: [ RISCV64 ]
         compiler: [gcc, llvm]
+        exclude:
+          arch: RISCV64
         include:
           - arch: RISCV64_CHERI
             compiler: llvm