[gcc(refs/users/aoliva/heads/testme)] add -mfloat128 to __float128-using test missing it

[Alexandre Oliva <aoliva@gcc.gnu.org>]

https://gcc.gnu.org/g:54a39afdf8edcbb82cdd3cfd26edc1f6d3c6a5dd

commit 54a39afdf8edcbb82cdd3cfd26edc1f6d3c6a5dd
Author: Alexandre Oliva <oliva@adacore.com>
Date:   Mon Mar 8 23:22:51 2021 -0300

    add -mfloat128 to __float128-using test missing it
    
    Most (all?) powerpc tests that use the __float128 type either enable
    it with -mfloat128, or use effective target requirements to check for
    its presence.
    
    prefix-ds-dq.c is failing in some of our configurations because it
    uses the __float128 type without checking for it, or enabling it
    explicitly.
    
    Since it's a compile test, I'm enabling it explicitly.
    
    
    for  gcc/testsuite/ChangeLog
    
            * gcc.target/powerpc/prefix-ds-dq.c: Enable __float128.

Diff:
---
 gcc/testsuite/gcc.target/powerpc/prefix-ds-dq.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/gcc/testsuite/gcc.target/powerpc/prefix-ds-dq.c b/gcc/testsuite/gcc.target/powerpc/prefix-ds-dq.c
index 554cd0c1bea..6517eadf44c 100644
--- a/gcc/testsuite/gcc.target/powerpc/prefix-ds-dq.c
+++ b/gcc/testsuite/gcc.target/powerpc/prefix-ds-dq.c
@@ -1,7 +1,8 @@
 /* { dg-do compile } */
 /* { dg-require-effective-target powerpc_prefixed_addr } */
 /* { dg-require-effective-target lp64 } */
-/* { dg-options "-O2 -mdejagnu-cpu=power10" } */
+/* { dg-options "-O2 -mdejagnu-cpu=power10 -mfloat128" } */
+/* { dg-prune-output ".-mfloat128. option may not be fully supported" } */
 
 /* Tests whether we generate a prefixed load/store operation for addresses that
    don't meet DS/DQ offset constraints.  64-bit is needed for testing the use