[committed] libstdc++: Compile PR93978 testcase with -Wall

[Patrick Palka]

Now that the frontend issue PR c++/94038 is thoroughly fixed, the
testcase for PR93978 no longer fails to compile with -O -Wall, so add
-Wall to the testcase's compile flags to help ensure we don't regress
here.

Committed as obvious after testing on x86_64-pc-linux-gnu.

libstdc++-v3/ChangeLog:

	PR libstdc++/93978
	* testsuite/std/ranges/adaptors/93978.cc: Add -Wall to
	dg-additional-options.  Avoid unused-but-set-variable warning.
---
 libstdc++-v3/testsuite/std/ranges/adaptors/93978.cc | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/93978.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/93978.cc
index a0152ec0532..82b82b0a5be 100644
--- a/libstdc++-v3/testsuite/std/ranges/adaptors/93978.cc
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/93978.cc
@@ -16,7 +16,7 @@
 // <http://www.gnu.org/licenses/>.
 
 // { dg-options "-std=gnu++2a" }
-// { dg-additional-options "-O" }
+// { dg-additional-options "-O -Wall" }
 // { dg-do compile { target c++2a } }
 
 #include <ranges>
@@ -25,11 +25,12 @@
 namespace ranges = std::ranges;
 namespace views = std::views;
 
-void
+auto
 test()
 {
   std::vector<std::string> x = {""};
   auto i = std::counted_iterator(x.begin(), 1);
   auto r = ranges::subrange{i, std::default_sentinel};
   auto v = r | views::join;
+  return v;
 }
-- 
2.27.0.rc1.5.gae92ac8ae3