[gcc r17-530] libstdc++: Use IANA name for ISO-8859-1 in format tests.

[Tomasz Kaminski]

https://gcc.gnu.org/g:c30a026bebebd19db124f60412f3ddcab291c900

commit r17-530-gc30a026bebebd19db124f60412f3ddcab291c900
Author: Tomasz Kamiński <tkaminsk@redhat.com>
Date:   Fri May 15 11:53:51 2026 +0200

    libstdc++: Use IANA name for ISO-8859-1 in format tests.
    
    Use IANA name for ISO-8859-1 as "-fexec-charset=" and add dg-require-iconv,
    to make sure it is supported.
    
    libstdc++-v3/ChangeLog:
    
            * testsuite/std/format/debug_nonunicode.cc: Pass ISO-8859-1 as
            exec-charset and make sure that it is supported.
            * testsuite/std/format/fill_nonunicode.cc: Likewise.

Diff:
---
 libstdc++-v3/testsuite/std/format/debug_nonunicode.cc | 3 ++-
 libstdc++-v3/testsuite/std/format/fill_nonunicode.cc  | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/testsuite/std/format/debug_nonunicode.cc b/libstdc++-v3/testsuite/std/format/debug_nonunicode.cc
index 2ac7e757ea8d..de70f55f14a9 100644
--- a/libstdc++-v3/testsuite/std/format/debug_nonunicode.cc
+++ b/libstdc++-v3/testsuite/std/format/debug_nonunicode.cc
@@ -1,4 +1,5 @@
-// { dg-options "-fexec-charset=ISO8859-1" }
+// { dg-options "-fexec-charset=ISO-8859-1" }
+// { dg-require-iconv "ISO-8859-1" }
 // { dg-do run { target c++23 } }
 // { dg-add-options no_pch }
 
diff --git a/libstdc++-v3/testsuite/std/format/fill_nonunicode.cc b/libstdc++-v3/testsuite/std/format/fill_nonunicode.cc
index 1370cf57ccdc..16d858c93a8d 100644
--- a/libstdc++-v3/testsuite/std/format/fill_nonunicode.cc
+++ b/libstdc++-v3/testsuite/std/format/fill_nonunicode.cc
@@ -1,4 +1,5 @@
-// { dg-options "-fexec-charset=ISO8859-1" }
+// { dg-options "-fexec-charset=ISO-8859-1" }
+// { dg-require-iconv "ISO-8859-1" }
 // { dg-do run { target c++20 } }
 // { dg-add-options no_pch }