[gcc r16-6678] toplevel: Unbreak Ada build [PR123490]

[Jakub Jelinek]

https://gcc.gnu.org/g:5079424ade2deddfa8d39a48a892f60679e4e32d

commit r16-6678-g5079424ade2deddfa8d39a48a892f60679e4e32d
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Sat Jan 10 11:36:25 2026 +0100

    toplevel: Unbreak Ada build [PR123490]
    
    As written earlier, the config-ml.in change from the
    --with-multi-buildlist patch broke build of Ada, Ada uses
    RTSDIR = rts$(subst /,_,$(MULTISUBDIR))
    and expects that the primary multilib will result in rts
    rather than rts_. it results in after the --with-multi-buildlist
    changes.
    
    The following patch fixes it by restoring previous behavior for
    ml_subdir / MULTISUBDIR such that for primary multilib it is
    still empty rather than /.
    
    2026-01-10  Jakub Jelinek  <jakub@redhat.com>
    
            PR ada/123490
            * config-ml.in: Restore ml_subdir being empty instead of /.
            for the primary multilib.

Diff:
---
 config-ml.in | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/config-ml.in b/config-ml.in
index 22021a7fe3c8..3b0440f3bd27 100644
--- a/config-ml.in
+++ b/config-ml.in
@@ -615,7 +615,11 @@ fi
 
 if [ -z "${with_multisubdir}" ]; then
   ml_top_subdir=`${CC-gcc} --print-multi-directory 2>/dev/null`
-  ml_subdir=/$ml_top_subdir
+  if [ "$ml_top_subdir" = . ]; then
+    ml_subdir=
+  else
+    ml_subdir=/$ml_top_subdir
+  fi
   ml_builddotdot=
   : # ml_srcdotdot= # already set
 else