FFI: Record simple C function calls.

Only handles cdecl and fixarg C functions.
Doesn't handle pass-by-value aggregates.
Doesn't handle 64 bit args/returns on 32 bit CPUs.

src/lj_traceerr.h

@@ -37,6 +37,7 @@ TREDEF(NYITMIX,	"NYI: mixed sparse/dense table")
 /* Recording C data operations. */
 TREDEF(NOCACHE,	"symbol not in cache")
 TREDEF(NYICONV,	"NYI: unsupported C type conversion")
+TREDEF(NYICALL,	"NYI: unsupported C function type")
 
 /* Optimizations. */
 TREDEF(GFAIL,	"guard would always fail")