cpu-all.h: define CPU_LDoubleU

Add a CPU_LDoubleU type, matching the floatx80 definition and the long
double type on x86 hosts.

Based on a patch from Laurent Vivier <laurent@vivier.eu>.

Cc: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

cpu-all.h

@@ -138,6 +138,16 @@ typedef union {
     uint64_t ll;
 } CPU_DoubleU;
 
+#if defined(FLOATX80)
+typedef union {
+     floatx80 d;
+     struct {
+         uint64_t lower;
+         uint16_t upper;
+     } l;
+} CPU_LDoubleU;
+#endif
+
 #if defined(CONFIG_SOFTFLOAT)
 typedef union {
     float128 q;