Include __mulodi4 in libor_ctime when it fixes clang -m32 -ftrapv

We use a pretty specific pair of autoconf tests here to make sure
that we only add this code when:
   a) a 64-bit signed multiply fails to link,
 AND
   b) the same 64-bit signed multiply DOES link correctly when
      __mulodi4 is defined.

Closes ticket 19079.

src/common/include.am

@@ -62,7 +62,14 @@ else
 readpassphrase_source=
 endif
 
+if ADD_MULODI4
+mulodi4_source=src/ext/mulodi/mulodi4.c
+else
+mulodi4_source=
+endif
+
 LIBOR_CTIME_A_SRC = \
+   $(mulodi4_source) \
    src/ext/csiphash.c   \
    src/common/di_ops.c