support floating point environment (fenv) on armhf (hard float) subarchs

patch by nsz. I've tested it on an armhf machine and it seems to be
working correctly.

arch/arm/bits/fenv.h

@@ -1,5 +1,18 @@
+#ifdef __SOFTFP__
 #define FE_ALL_EXCEPT 0
 #define FE_TONEAREST  0
+#else
+#define FE_INVALID    1
+#define FE_DIVBYZERO  2
+#define FE_OVERFLOW   4
+#define FE_UNDERFLOW  8
+#define FE_INEXACT    16
+#define FE_ALL_EXCEPT 31
+#define FE_TONEAREST  0
+#define FE_DOWNWARD   0x800000
+#define FE_UPWARD     0x400000
+#define FE_TOWARDZERO 0xc00000
+#endif
 
 typedef unsigned long fexcept_t;