Fix architecture detection when MinGW is 32 while host is 64.

CPackDetectArch.cmake

@@ -9,11 +9,17 @@ SET (ARCHITECTURE "${CUSTOM_ARCHITECTURE}")
 IF (ARCHITECTURE STREQUAL "")
     # SET (ARCHITECTURE "${CMAKE_SYSTEM_PROCESSOR}")
     # SET (ARCHITECTURE "${CMAKE_HOST_SYSTEM_PROCESSOR}")
-    EXECUTE_PROCESS(COMMAND uname -m COMMAND tr -d '\n' OUTPUT_VARIABLE ARCHITECTURE)
+    IF (WIN32)
+        EXECUTE_PROCESS(COMMAND uname -s COMMAND tr -d '\n' OUTPUT_VARIABLE ARCHITECTURE)
+    ELSE (WIN32)
+      EXECUTE_PROCESS(COMMAND uname -m COMMAND tr -d '\n' OUTPUT_VARIABLE ARCHITECTURE)
+    ENDIF (WIN32)
 
     # Replacements
     STRING (REGEX REPLACE "^x86_64$" "amd64" ARCHITECTURE "${ARCHITECTURE}")
+    STRING (REGEX REPLACE "MINGW64.*" "amd64" ARCHITECTURE "${ARCHITECTURE}")
     STRING (REGEX REPLACE "^i.86$" "i386" ARCHITECTURE "${ARCHITECTURE}")
+    STRING (REGEX REPLACE "MINGW32.*" "i386" ARCHITECTURE "${ARCHITECTURE}")
     STRING (REGEX REPLACE "^armv7l$" "armel" ARCHITECTURE "${ARCHITECTURE}")
 
 ENDIF ()