Another step towards detecting if _REENTRANT is already defined or actually

needed, and being able to define it if appropriate for further configure tests
as well as for the generated config file.

Introduced reentrant.m4 intended for our reentrant related autotools/m4 macros.

buildconf

@@ -209,6 +209,7 @@ PERL=`findtool ${PERL:-perl}`
 echo "buildconf: running libtoolize"
 $libtoolize --copy --automake --force || die "The libtoolize command failed"
 echo "buildconf: running aclocal"
+ACLOCAL_FLAGS="-I . $ACLOCAL_FLAGS"
 ${ACLOCAL:-aclocal} $ACLOCAL_FLAGS || die "The aclocal command line failed"
 if test -n "$PERL"; then
   echo "buildconf: running aclocal hack to convert all mv to mv -f"