Disable C extension to avoid miscompilation.

Author: dvc94ch

riscv32imac-unknown-none.json

@@ -6,7 +6,7 @@
     "arch": "riscv",
     "os": "none",
     "cpu": "generic-rv32",
-    "features": "+m,+a,+c",
+    "features": "+m,+a",
     "max-atomic-width": 32,
     "target-c-int-width": "32",
     "linker": "ld.lld",