[gcc r16-650] libstdc++: build testsuite with -Wabi

[Jason Merrill]

https://gcc.gnu.org/g:f28ff1e4f1c91f46d80e26dd77917e47cdd41bbe

commit r16-650-gf28ff1e4f1c91f46d80e26dd77917e47cdd41bbe
Author: Jason Merrill <jason@redhat.com>
Date:   Thu May 1 10:20:25 2025 -0400

    libstdc++: build testsuite with -Wabi
    
    I added this locally to check whether the PR120012 fix affects libstdc++ (it
    doesn't) but it seems more generally useful to catch whether compiler
    ABI changes have library impact.
    
    libstdc++-v3/ChangeLog:
    
            * testsuite/lib/libstdc++.exp: Add -Wabi.

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

diff --git a/libstdc++-v3/testsuite/lib/libstdc++.exp b/libstdc++-v3/testsuite/lib/libstdc++.exp
index fbc9f7f13e64..da1f4245e4b8 100644
--- a/libstdc++-v3/testsuite/lib/libstdc++.exp
+++ b/libstdc++-v3/testsuite/lib/libstdc++.exp
@@ -586,6 +586,7 @@ proc v3_target_compile { source dest type options } {
     global tool
 
     lappend options "additional_flags=-fdiagnostics-plain-output"
+    lappend options "additional_flags=-Wabi=20";
 
     if { [target_info needs_status_wrapper] != "" && [info exists gluefile] } {
 	lappend options "libs=${gluefile}"