re PR target/58330 (powerpc64 atomic store split in two)

PR target/58330
oops, missed from commit

From-SVN: r202428

gcc/testsuite/gcc.target/powerpc/pr58330.c

+/* { dg-do compile { target { powerpc*-*-* } } } */
+/* { dg-require-effective-target lp64 } */
+/* { dg-options "-O -mno-popcntb" } */
+/* { dg-final { scan-assembler-not "stwbrx" } } */
+
+void
+write_reverse (unsigned long *addr, unsigned long val)
+{
+  unsigned long reverse = __builtin_bswap64 (val);
+  __atomic_store_n (addr, reverse, __ATOMIC_RELAXED);
+}