py: If setjmp NLR implementation is forced, omit native versions.

py/nlrthumb.S

-#ifdef __thumb2__
+#if defined(__thumb2__) && !MICROPY_NLR_SETJMP
 /* thumb callee save: bx, bp, sp, r12, r14, r14, r15 */
 
     .syntax unified

py/nlrx64.S

-#ifdef __x86_64__
+#if defined(__x86_64__) && !MICROPY_NLR_SETJMP
 /* x64 callee save: bx, bp, sp, r12, r13, r14, r15 */
 
     .file   "nlr.s"

py/nlrx86.S

-#ifdef __i386__
+#if defined(__i386__) && !MICROPY_NLR_SETJMP
 /* x86 callee save: bx, di, si, bp, sp */
 
     .file   "nlr.s"