- change sys/reent.h to replace _REENT_CHECK_DEBUG with
_REENT_CHECK_VERIFY which when set asserts that any memory
allocated is non-NULL and calls __assert_func directly
- add new --enable-newlib-reent-check-verify configure option
- add support for configure.host to specify default for
newlib_reent_check_verify
- add _REENT_CHECK_VERIFY macro support to acconfig.h and newlib.hin