modules/hal/openisa: Support building without -ffreestanding

With -ffreestanding disabled, Zephyr SDK 0.15.0 generates a potentially
uninitialized variable warning that appears to be a false positive. Disable
the warning around the affected code.

Signed-off-by: Keith Packard <keithp@keithp.com>

Author: keith-packard

west.yml

@@ -98,7 +98,7 @@ manifest:
       groups:
         - hal
     - name: hal_openisa
-      revision: 40d049f69c50b58ea20473bee14cf93f518bf262
+      revision: pull/7/head
       path: modules/hal/openisa
       groups:
         - hal