Don't compile C code as C++ any more with MSVC.

Visual Studio 2015 can compile the tun2socks part of the code at least as C.

CMakeLists.txt

@@ -131,7 +131,7 @@ if (NOT (SIZE_SIZE GREATER INT_SIZE OR SIZE_SIZE EQUAL INT_SIZE))
 endif ()
 
 if (MSVC)
-    add_definitions(/TP -D_CRT_SECURE_NO_WARNINGS /wd4065 /wd4018 /wd4533 /wd4244 /wd4102)
+    add_definitions(-D_CRT_SECURE_NO_WARNINGS /wd4065 /wd4018 /wd4533 /wd4244 /wd4102)
 else ()
     add_definitions(-std=gnu99 -Wall -Wno-unused-value -Wno-parentheses -Wno-switch -Wredundant-decls -Wshadow)