src/jv_dtoa.c: Fix compiler error

Author: UlrichEckhardt

src/jv_dtoa.c

@@ -299,7 +299,7 @@ extern "C" {
 #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;