[bug#72225] [PATCH] _AM_PROG_CC_C_O: clean up after .dSYM directories properly

On darwin, the compiler will generate .dSYM directories (for debug
info) alongside executables when invoked, leading to messages like the
following in configure output:

checking whether /usr/local/bin/gcc understands -c and -o together...
rm: conftest.dSYM: is a directory
yes

The attached patch ought to fix this by passing the -r flag to the rm
invocation that's meant to clean up the conftests. One concern,
though, is that in the same invocation, it also tries to remove
anything called "core", so I worry what might happen with this change
if "core" happens to be a directory... should I handle that
separately?
Thanks,
Eric Gallager

diff --git a/m4/prog-cc-c-o.m4 b/m4/prog-cc-c-o.m4
index a31a4a414..fe388203d 100644
--- a/m4/prog-cc-c-o.m4
+++ b/m4/prog-cc-c-o.m4
@@ -31,7 +31,7 @@ AC_CACHE_CHECK(
       break
     fi
   done
-  rm -f core conftest*
+  rm -rf core conftest*
   unset am_i])
 if test "$am_cv_prog_cc_c_o" != yes; then
    # Losing compiler, so override with the script.