Bug 1331954 - Put forgotten #error directive to dtoa.c. r=arai

There was some incorrect error handling in file dtoa.c, I just
put forgotten #error directive

MozReview-Commit-ID: 2zzwI0YAFpI

js/src/dtoa.c

@@ -253,7 +253,7 @@ extern void *MALLOC(size_t);
 #endif
 
 #if defined(IEEE_8087) + defined(IEEE_MC68k) + defined(VAX) + defined(IBM) != 1
-Exactly one of IEEE_8087, IEEE_MC68k, VAX, or IBM should be defined.
+#error "Exactly one of IEEE_8087, IEEE_MC68k, VAX, or IBM should be defined."
 #endif
 
 typedef union { double d; ULong L[2]; } U;