Clean up when checking for the MPI workarounds.

* Let AC_COMPILE_IFELSE clean up by postponing the loop break.
* AC_COMPILE_IFELSE without the first argument does not remove the
  source file.

m4/acx_mpich34_hindexed_workaround.m4

@@ -104,7 +104,9 @@ extern pthread_mutex_t yaksui_atomic_mutex;],
      [acx_yaksa_add_workaround="$acx_yaksa_add_workaround/xt_yaksa_indexed.c"
       mv conftest.c "$acx_yaksa_add_workaround"
       ACX_MV_OBJ([conftest],[mpich_workaround])],
-     [is_affected_mpich=false ; break])
+     [is_affected_mpich=false
+      rm -f conftest.$ac_ext])
+   $is_affected_mpich || break
    dnl 4. verify listed tests now succeed
    CPPFLAGS=$acx_saved_CPPFLAGS
    LIBS="mpich_workaround.$ac_objext $LIBS"

m4/acx_ompi_dt_workaround.m4

@@ -151,7 +151,9 @@ s/^ *//;s/ *$//'`])
    as_dir=src as_fn_mkdir_p
    AC_COMPILE_IFELSE(,
      [ACX_MV_OBJ([conftest],[ompi_workaround])],
-     [is_affected_ompi=false ; break])
+     [is_affected_ompi=false])
+   rm -f conftest.$ac_ext
+   $is_affected_ompi || break
    dnl 4. verify listed tests now succeed
    CPPFLAGS=$acx_saved_CPPFLAGS
    CFLAGS=$acx_saved_CFLAGS