[Bug other/121998] New: --disable-multilib doesn't work if provision for multilib has been made.

[mark.dunn.and.sharon.king at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121998

            Bug ID: 121998
           Summary: --disable-multilib doesn't work if provision for
                    multilib has been made.
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mark.dunn.and.sharon.king at gmail dot com
  Target Milestone: ---

I am using a raspberry PI5 (aarch64-linux-gnu). It uses a Debian based OS
(multiarch not multilib). For embedded work I require simplicity and therefor a
single architecture. \lib32 and \lib64 create a level of complexity I do not
want. 
The commands I used were:
export CFLAGS="--sysroot=$UNSTABLE_ISOLATED_SYSROOT"
export LDFLAGS=" \
        --sysroot=$UNSTABLE_ISOLATED_SYSROOT \
       
-Wl,--dynamic-linker=$UNSTABLE_ISOLATED_PREFIX/lib/ld-linux-aarch64.so.1"
export CXXFLAGS=$CFLAGS

mkdir -p $UNSTABLE_ISOLATED_BUILD/gcc
cd $UNSTABLE_ISOLATED_BUILD/gcc

$SOURCE/gcc/configure \
        --build=$PI_TRIPLET \
        --host=$PI_TRIPLET \
        --disable-libquadmath \
        --disable-nls \
        --disable-multilib \
        --enable-bootstrap \
        --enable-languages=c,c++ \
        --prefix=$UNSTABLE_ISOLATED_PREFIX \
        --with-cpu=cortex-a76+crypto \
        --with-glibc-version=2.42 \
        --with-multiarch-dir=$PI_TRIPLET \
        --with-sysroot=$UNSTABLE_ISOLATED_SYSROOT \
        --with-tune=cortex-a76
make -j$(nproc)
make install

If MULTILIB_OSDIRNAMES has been set then multilib cannot be disabled.
I fixed it in gcc/Makefile.in but recognise that gcc/Makfile.in is created from
further up the chain. I lack the understanding as to what fixes that to fix
this:

diff --git a/gcc/Makefile.in b/gcc/Makefile.in
index 4503dab6037..742a4ea1761 100644
--- a/gcc/Makefile.in
+++ b/gcc/Makefile.in
@@ -2498,8 +2498,7 @@ libgcc.mvars: config.status Makefile specs xgcc$(exeext)
 # switches.
 multilib.h: s-mlib; @true
 s-mlib: $(srcdir)/genmultilib Makefile
-       if test @enable_multilib@ = yes \
-          || test -n "$(MULTILIB_OSDIRNAMES)"; then \
+    if test @enable_multilib@ = yes; then \
          $(SHELL) $(srcdir)/genmultilib \
            "$(MULTILIB_OPTIONS)" \
            "$(MULTILIB_DIRNAMES)" \
@@ -2513,7 +2512,7 @@ s-mlib: $(srcdir)/genmultilib Makefile
            "$(MULTILIB_REUSE)" \
            "@enable_multilib@" \
            > tmp-mlib.h; \
-       else \
+    elif test -n "$(MULTILIB_OSDIRNAMES)"; then \
          $(SHELL) $(srcdir)/genmultilib '' '' '' '' '' '' '' '' \
            "$(MULTIARCH_DIRNAME)" '' no \
            > tmp-mlib.h; \