Bug 538056 - Signal handler for FPU exception is broken for Windows x64, r=m_kato,bsmedberg

toolkit/xre/nsSigHandlers.h:
	define x86 constants also for msvc x86-64

toolkit/xre/nsSigHandlers.cpp:
	Take into account different structure names for win64

toolkit/xre/nsSigHandlers.cpp

@@ -399,8 +399,13 @@ void InstallSignalHandlers(const char *ProgramName)
 
 #if defined(_M_IX86) || defined(_M_X64)
 
+#ifdef _M_X64
+#define X87CW(ctx) (ctx)->FltSave.ControlWord
+#define X87SW(ctx) (ctx)->FltSave.StatusWord
+#else
 #define X87CW(ctx) (ctx)->FloatSave.ControlWord
 #define X87SW(ctx) (ctx)->FloatSave.StatusWord
+#endif
 
 /*
  * SSE traps raise these exception codes, which are defined in internal NT headers

toolkit/xre/nsSigHandlers.h

@@ -36,7 +36,7 @@
  *
  * ***** END LICENSE BLOCK ***** */
 
-#if defined(_M_IX86) || defined(__i386__) || defined(__i386) || defined(__amd64__)
+#if defined(_M_IX86) || defined(_M_X64) || defined(__i386__) || defined(__i386) || defined(__amd64__)
 
 /*
  * x87 FPU Control Word: