[gcc r16-6183] libstdc++: Update default -std for testsuite

[Jonathan Wakely]

https://gcc.gnu.org/g:e0fa6ea45fbd0280ace8803db1bc30a7d069da9e

commit r16-6183-ge0fa6ea45fbd0280ace8803db1bc30a7d069da9e
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon Dec 15 16:00:20 2025 +0000

    libstdc++: Update default -std for testsuite
    
    libstdc++-v3/ChangeLog:
    
            * testsuite/lib/libstdc++.exp (dg-v3-runtest) Set default_std to
            20.
    
    Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>

Diff:
---
 libstdc++-v3/testsuite/lib/libstdc++.exp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libstdc++-v3/testsuite/lib/libstdc++.exp b/libstdc++-v3/testsuite/lib/libstdc++.exp
index b1593e42f941..b11f4a34dfa1 100644
--- a/libstdc++-v3/testsuite/lib/libstdc++.exp
+++ b/libstdc++-v3/testsuite/lib/libstdc++.exp
@@ -533,7 +533,7 @@ proc v3-dg-runtest { testcases flags default-extra-flags } {
 		# single test.
 		# These should be adjusted whenever the default -std is
 		# updated or newer C++ effective target is added.
-		set default_std 17
+		set default_std 20
 		set max_std 26
 		set min_std [v3-minimum-std $test $default_std $max_std]
 		if { $min_std > $default_std } {