Merge pull request #3708 from sschuberth/master

CMakeLists: Further improve the error messages regarding CMAKE_SIZEOF_VOID_P

CMakeLists.txt

@@ -580,8 +580,10 @@ IF (CMAKE_SIZEOF_VOID_P EQUAL 8)
 	ADD_DEFINITIONS(-DGIT_ARCH_64)
 ELSEIF (CMAKE_SIZEOF_VOID_P EQUAL 4)
 	ADD_DEFINITIONS(-DGIT_ARCH_32)
-ELSE()
+ELSEIF (CMAKE_SIZEOF_VOID_P)
 	MESSAGE(FATAL_ERROR "Unsupported architecture (pointer size is ${CMAKE_SIZEOF_VOID_P} bytes)")
+ELSE()
+	MESSAGE(FATAL_ERROR "Unsupported architecture (CMAKE_SIZEOF_VOID_P is unset)")
 ENDIF()
 
 # Compile and link libgit2