Silence bogus -Werror=clobbered (GCC 7 --enable-optimized)

> In file included from gcc/include/c++/7.1.1/vector:69:0,
>                  from jvmfwk/plugins/sunmajor/pluginlib/sunjavaplugin.cxx:39:
> gcc/include/c++/7.1.1/bits/vector.tcc: In function ‘javaPluginError jfw_plugin_startJavaVirtualMachine(const JavaInfo*, const JavaVMOption*, sal_Int32, JavaVM**, JNIEnv**)’:
> gcc/include/c++/7.1.1/bits/vector.tcc:407:15: error: variable ‘__new_finish’ might be clobbered by ‘longjmp’ or ‘vfork’ [-Werror=clobbered]
>        pointer __new_finish(__new_start);
>                ^~~~~~~~~~~~

Change-Id: Iefabac65871ed79bcfa333f0193fcbbd1369f7f1
Reviewed-on: https://gerrit.libreoffice.org/66714
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
(cherry picked from commit 58f30cf1)

jvmfwk/plugins/sunmajor/pluginlib/sunjavaplugin.cxx

@@ -848,7 +848,14 @@ javaPluginError jfw_plugin_startJavaVirtualMachine(
 #endif
 
    return errorcode;
+#if defined __GNUC__ && __GNUC__ == 7 && !defined __clang__
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wclobbered"
+#endif
 }
+#if defined __GNUC__ && __GNUC__ == 7 && !defined __clang__
+#pragma GCC diagnostic pop
+#endif
 
 javaPluginError jfw_plugin_existJRE(const JavaInfo *pInfo, bool *exist)
 {