From 4dae190d330f94148fc4121b8d662af26f091f8a Mon Sep 17 00:00:00 2001
From: wkliao <wkliao@users.noreply.github.com>
Date: Thu, 16 Apr 2026 11:17:50 -0500
Subject: [PATCH] Add --tag=CC option to libtool compile and link command lines

When using autoconf (GNU Autoconf) 2.73, an error message is shown:
configure:37480: ./libtool --mode=compile
/Users/runner/work/PnetCDF/PnetCDF/MPI/bin/mpicc -c -g -O2  conftest.c
-o conftest.lo >&5
libtool: compile: unable to infer tagged configuration
libtool:   error: specify a tag with '--tag'
---
 m4/check_mpi.m4 | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/m4/check_mpi.m4 b/m4/check_mpi.m4
index 3fdcb8867..ff8caa977 100644
--- a/m4/check_mpi.m4
+++ b/m4/check_mpi.m4
@@ -206,8 +206,9 @@ AC_DEFUN([LT_MPI_CHECK_SHLIB],[
    if test "x$RM" = xrm || test "x$RM" = "x/bin/rm" ; then
       RM="$RM -f"
    fi
-   ac_ltcompile='./libtool --mode=compile $MPICC -c $CFLAGS $CPPFLAGS conftest.$ac_ext -o conftest.lo >&AS_MESSAGE_LOG_FD'
-   ac_ltlink_la='./libtool --mode=link $MPICC -rpath `pwd` $CFLAGS $LDFLAGS -o libconftest.la conftest.lo $LIBS >&AS_MESSAGE_LOG_FD'
+   # must add '--tag=CC', otherwise autotool 2.73 failed.
+   ac_ltcompile='./libtool --tag=CC --mode=compile $MPICC -c $CFLAGS $CPPFLAGS conftest.$ac_ext -o conftest.lo >&AS_MESSAGE_LOG_FD'
+   ac_ltlink_la='./libtool --tag=CC --mode=link $MPICC -rpath `pwd` $CFLAGS $LDFLAGS -o libconftest.la conftest.lo $LIBS >&AS_MESSAGE_LOG_FD'
    AS_IF([AC_TRY_EVAL([ac_ltcompile]) &&
        AC_TRY_EVAL([ac_ltlink_la]) &&
        AC_TRY_COMMAND([test -s libconftest.la])],