Try using clang

Originally I didn't do this as it seems the linker step uses gcc
regardless. But it seems better to be consistent with the other C repos.

Note it's still the case that the linker step appears to use gcc, but
I'm choosing to believe that's okay.

Author: horgh

.github/workflows/address-sanitizer.yml

@@ -9,6 +9,7 @@ jobs:
     name: Address Sanitizer
     runs-on: ubuntu-latest
     env:
+      CC: clang
       CFLAGS: -fsanitize=address
       LDFLAGS: -fsanitize=address
     steps: