Revert "[ASan/Win] Remove a hack that seems not to be required with VS2013 anymore" (r215708)

This is still needed for VS2012.

llvm-svn: 215930

compiler-rt/lib/sanitizer_common/sanitizer_printf.cc

@@ -22,6 +22,10 @@
 #include <stdio.h>
 #include <stdarg.h>
 
+#if SANITIZER_WINDOWS && !defined(va_copy)
+# define va_copy(dst, src) ((dst) = (src))
+#endif
+
 namespace __sanitizer {
 
 StaticSpinMutex CommonSanitizerReportMutex;