[gcc r13-4795] build: add -Wconditionally-supported to strict_warn [PR64867]

[gcc r13-4795] build: add -Wconditionally-supported to strict_warn [PR64867]

[Jason Merrill]

https://gcc.gnu.org/g:263c22a95bc9a0d80c4873c0291b0f938cea7310

commit r13-4795-g263c22a95bc9a0d80c4873c0291b0f938cea7310
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Dec 5 10:00:31 2022 -0500

    build: add -Wconditionally-supported to strict_warn [PR64867]
    
    The PR (which isn't resolved by this commit) pointed out to me that GCC
    should build with -Wconditionally-supported to support bootstrapping with a
    C++11 compiler that makes different choices.
    
            PR c++/64867
    
    gcc/ChangeLog:
    
            * configure.ac (strict_warn): Add -Wconditionally-supported.
            * configure: Regenerate.

Diff:
---
 gcc/configure.ac | 2 +-
 gcc/configure    | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/gcc/configure.ac b/gcc/configure.ac
index 5efbf11793c..b91f54ce05b 100644
--- a/gcc/configure.ac
+++ b/gcc/configure.ac
@@ -580,7 +580,7 @@ ACX_PROG_CC_WARNING_OPTS(
 	m4_quote(m4_do([-Wstrict-prototypes -Wmissing-prototypes ],
 		       [])), [c_loose_warn])
 ACX_PROG_CXX_WARNING_OPTS(
-	m4_quote(m4_do([-Wmissing-format-attribute ],
+	m4_quote(m4_do([-Wmissing-format-attribute ], [-Wconditionally-supported ],
 		       [-Woverloaded-virtual])), [strict_warn])
 ACX_PROG_CC_WARNING_OPTS(
 	m4_quote(m4_do([-Wold-style-definition -Wc++-compat])), [c_strict_warn])
diff --git a/gcc/configure b/gcc/configure
index 61b3cedbe69..921aad60712 100755
--- a/gcc/configure
+++ b/gcc/configure
@@ -7215,7 +7215,7 @@ ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
 
 strict_warn=
 save_CXXFLAGS="$CXXFLAGS"
-for real_option in -Wmissing-format-attribute -Woverloaded-virtual; do
+for real_option in -Wmissing-format-attribute -Wconditionally-supported -Woverloaded-virtual; do
   # Do the check with the no- prefix removed since gcc silently
   # accepts any -Wno-* option on purpose
   case $real_option in