Make c4script binary use our private getopt library if necessary

Systems that don't come with getopt/getopt_long in their runtime library
need to link to our private copy; link that and use the right const-ness
for its prototype.

CMakeLists.txt

@@ -1143,6 +1143,7 @@ target_compile_definitions(c4script PRIVATE "USE_CONSOLE")
 target_link_libraries(c4script
 	libmisc
 	libc4script
+	${GETOPT_LIBRARIES}
 )
 
 if(NOT HEADLESS_ONLY)

src/script/C4ScriptMain.cpp

@@ -27,7 +27,7 @@ int usage(const char *argv0)
 	return 1;
 }
 
-int main(int argc, char *const argv[])
+int main(int argc, char *argv[])
 {
 	if (argc < 2)
 		return usage(argv[0]);