Disable trace stitching (for now) due to a design mistake.

Thanks to Elias Hogstvedt for finding a test case for a well known,
but hard to track down issue with trace stitching.

src/lj_traceerr.h

@@ -24,6 +24,8 @@ TREDEF(BADTYPE,	"bad argument type")
 TREDEF(CJITOFF,	"JIT compilation disabled for function")
 TREDEF(CUNROLL,	"call unroll limit reached")
 TREDEF(DOWNREC,	"down-recursion, restarting")
+TREDEF(NYICF,	"NYI: C function %p")
+TREDEF(NYIFF,	"NYI: FastFunc %s")
 TREDEF(NYIFFU,	"NYI: unsupported variant of FastFunc %s")
 TREDEF(NYIRETL,	"NYI: return to lower frame")