py/nlrmips: Add native NLR support for MIPS architecture.

This can be tested using ports/minimal and qemu:

    make CC=mips-linux-gnu-gcc-8

Then run with qemu-mips:

    stty raw opost -echo;
    QEMU_LD_PREFIX=/usr/mips-linux-gnu/ qemu-mips build/firmware.elf;
    sleep 1; reset

Signed-off-by: Jan Willeke <willeke@smartmote.de>

py/py.cmake

@@ -53,6 +53,7 @@ set(MICROPY_SOURCE_PY
     ${MICROPY_PY_DIR}/mpz.c
     ${MICROPY_PY_DIR}/nativeglue.c
     ${MICROPY_PY_DIR}/nlr.c
+    ${MICROPY_PY_DIR}/nlrmips.c
     ${MICROPY_PY_DIR}/nlrpowerpc.c
     ${MICROPY_PY_DIR}/nlrsetjmp.c
     ${MICROPY_PY_DIR}/nlrthumb.c