AIX build fails: various unused variable and function warnings

We get a couple of warnings as errors on AIX :
/priv/jenkins/client-home/workspace/openjdk-jdk-dev-aix_ppc64-opt/jdk/src/java.base/unix/native/libjava/ProcessHandleImpl_unix.c:665:10: error: unused variable 'exePath' [-Werror,-Wunused-variable]
    char exePath[PATH_MAX];
         ^
/priv/jenkins/client-home/workspace/openjdk-jdk-dev-aix_ppc64-opt/jdk/src/java.base/unix/native/libjava/ProcessHandleImpl_unix.c:668:9: error: unused variable 'ret' [-Werror,-Wunused-variable]
    int ret;
        ^
/priv/jenkins/client-home/workspace/openjdk-jdk-dev-aix_ppc64-opt/jdk/src/java.base/unix/native/libjava/ProcessHandleImpl_unix.c:664:10: error: unused variable 'fn' [-Werror,-Wunused-variable]
    char fn[32];
         ^

This might be related to the make changes
8339156: Use more fine-granular clang unused warnings
https://bugs.openjdk.org/browse/JDK-8339156
(we use clang too on AIX)