[RS6000] biarch test fail

[Alan Modra]

I thought this one was worth at least commenting as to why it fails
when biarch testing.  OK?

	* gcc.target/powerpc/bswap64-4.c: Comment.

diff --git a/gcc/testsuite/gcc.target/powerpc/bswap64-4.c b/gcc/testsuite/gcc.target/powerpc/bswap64-4.c
index a3c05539652..11787000409 100644
--- a/gcc/testsuite/gcc.target/powerpc/bswap64-4.c
+++ b/gcc/testsuite/gcc.target/powerpc/bswap64-4.c
@@ -7,6 +7,12 @@
 /* { dg-final { scan-assembler-times "ldbrx" 1 { target has_arch_pwr7 } } } */
 /* { dg-final { scan-assembler-times "stdbrx" 1 { target has_arch_pwr7 } } } */
 
+/* This test will fail when biarch testing with
+   "RUNTESTFLAGS=--target_board=unix'{-m64,-m32}'" because the -m32 is
+   added on the command line after the dg-options -mpowerpc64, and
+   common/config/rs6000/rs6000-common.c:rs6000_handle_option disables
+   -mpowerpc64 for -m32.  */
+
 long long swap_load (long long *a) { return __builtin_bswap64 (*a); }
 long long swap_reg (long long a) { return __builtin_bswap64 (a); }
 void swap_store (long long *a, long long b) { *a = __builtin_bswap64 (b); }

-- 
Alan Modra
Australia Development Lab, IBM