Add /J to MSVC compile flags

http://msdn.microsoft.com/en-us/library/0d294k5z.aspx

/J (Default char Type Is unsigned)

Changes the default char type from signed char to unsigned char, and
the char type is zero-extended when it is widened to an int type.

source/compiler/CMakeLists.txt

@@ -24,7 +24,7 @@ IF(HAVE_ALLOCA_H)
 ENDIF(HAVE_ALLOCA_H)
 
 IF(MSVC)
-  ADD_DEFINITIONS(-D_CRT_SECURE_NO_WARNINGS)
+  ADD_DEFINITIONS(-D_CRT_SECURE_NO_WARNINGS /J)
 ENDIF(MSVC)
 
 IF(UNIX)