core: Add ctypes::c_char

Author: brson

src/libcore/ctypes.rs

@@ -5,7 +5,7 @@ FIXME: Add a test that uses some native code to verify these sizes,
 which are not obviously correct for all potential platforms.
 */
 
-export c_int, c_uint, long, longlong, unsigned, ulong, ulonglong;
+export c_char, c_int, c_uint, long, longlong, unsigned, ulong, ulonglong;
 export intptr_t, uintptr_t;
 export uint32_t;
 export void::{};
@@ -16,6 +16,9 @@ export enum;
 
 // PORT adapt to architecture
 
+#[doc = "A signed integer with the same size as a C `char`."]
+type c_char = i8;
+
 #[doc(
   brief = "A signed integer with the same size as a C `int`."
 )]