add powerpc soft-float support

Some PowerPC CPUs (e.g. Freescale MPC85xx) have a completely different
instruction set for floating point operations (SPE).
Executing regular PowerPC floating point instructions results in
"Illegal instruction" errors.

Make it possible to run these devices in soft-float mode.

arch/powerpc/bits/fenv.h

@@ -1,3 +1,7 @@
+#ifdef _SOFT_FLOAT
+#define FE_ALL_EXCEPT 0
+#define FE_TONEAREST  0
+#else
 #define FE_TONEAREST	0
 #define FE_TOWARDZERO	1
 #define FE_UPWARD	2
@@ -24,6 +28,7 @@
 
 #define FE_ALL_INVALID		0x01f80700
 #endif
+#endif
 
 typedef unsigned fexcept_t;
 typedef double fenv_t;