mpfr 3.1.2 references these symbols and fails if they're not defined.

Index: mingw-w64-headers/crt/float.h
===================================================================
--- mingw-w64-headers/crt.orig/float.h	2012-07-17 11:03:12.000000000 +0000
+++ mingw-w64-headers/crt/float.h	2013-08-13 08:23:20.000000000 +0000
@@ -111,6 +111,9 @@
 	#define FLT_ROUNDS 1
     
 	#define _FLOAT_H___
+
+	#define DBL_EPSILON __DBL_EPSILON__
+	#define FLT_EPSILON __FLT_EPSILON__
 #endif
 #endif
 #endif