hotfix: make ifx work with autoconf <= 2.69 in Spack (#22683)

Autoconf before 2.70 will erroneously pass ifx's -loopopt argument to the
linker, requiring all packages to use autoconf 2.70 or newer to use ifx.

This is a hotfix enabling ifx to be used in Spack. Instead of bothering
to upgrade autoconf for every package, we'll just strip out the
problematic flag if we're in `ld` mode.

- [x] Add a conditional to the `cc` wrapper to skip `-loopopt` in `ld`
      mode. This can probably be generalized in the future to strip more
      things (e.g., via an environment variable we can constrol from
      Spack) but it's good enough for now.

- [x] Add a test ensuring that `-loopopt` arguments are stripped in link
      mode, but not in compile mode.

lib/spack/env/cc

@@ -311,6 +311,14 @@ while [ -n "$1" ]; do
             fi
             ;;
         -l*)
+            # -loopopt=0 is passed to the linker erroneously in
+            # autoconf <= 2.69. Filter it out.
+            # TODO: generalize filtering of args with an env var, so that
+            # TODO: we do not have to special case this here.
+            if [ "$mode" = "ld" ] && [ "$1" != "${1#-loopopt}" ]; then
+                shift
+                continue
+            fi
             arg="${1#-l}"
             if [ -z "$arg" ]; then shift; arg="$1"; fi
             other_args+=("-l$arg")