Error-out on --enable-ld with path and gcc

Now that mold can successfully link LO and its unit tests (needs
mold 1.0.1 or later), gcc could support an alternative linker
with '-B<path>' to search for its tools in some extra path.

But it turns out that libtool filters the '-B' option from its
arguments, so it falls back to some system ld. But since we
already tested "our" ld for some features, this might not match,
resulting in libtool failing to link externals, like orcus.

The original use case was testing mold, which can also be done
by using LD_PRELOAD=/usr/lib/mold/mold-wrapper.so, so this patch
just shows an error, if gcc is used with an use_ld_path.

Change-Id: I9c7860895f8b24a5f3fc4b1e0fd5232be22293f8
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/127493
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>

1 files changed, 9 insertions, 1 deletions

diff --git a/configure.ac b/configure.ac
index fb8d85a01f71..2467b55957a9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -4500,7 +4500,15 @@ check_use_ld()
     use_ld=-fuse-ld=${1%%:*}
     use_ld_path=${1#*:}
     if test "$use_ld_path" != "$1"; then
-        use_ld="$use_ld --ld-path=$use_ld_path"
+        if test "$COM_IS_CLANG" = TRUE; then
+            use_ld="${use_ld} --ld-path=${use_ld_path}"
+        else
+            # I tried to use gcc's '-B<path>' and a directory + symlink setup in
+	    # $BUILDDIR, but libtool always filtered-out that option, so gcc wouldn't
+	    # pickup the alternative linker, when called by libtool for linking.
+            # For mold, one can use LD_PRELOAD=/usr/lib/mold/mold-wrapper.so instead.
+	    AC_MSG_ERROR([A linker path is just supported with clang, because of libtool's -B filtering!])
+        fi
     fi
     use_ld_fail_if_error=$2
     use_ld_ok=