dynload: use c_char instead of i8 for dlopen argument

Signed-off-by: Bo YU <yubo@iscas.ac.cn>

Author: yuzibo

gccjit_sys/src/dynload.rs

@@ -8,7 +8,7 @@ mod platform {
 
     #[link(name="dl")]
     extern "C" {
-        fn dlopen(filename: *const i8, flag: c_int) -> *mut c_void;
+        fn dlopen(filename: *const c_char, flag: c_int) -> *mut c_void;
         fn dlsym(handle: *mut c_void, symbol: *const i8) -> *mut c_void;
         fn dlclose(handle: *mut c_void) -> c_int;
         fn dlerror() -> *const c_char;