Add support for darwin to core:c/libc

core/c/libc/stdlib.odin

@@ -4,6 +4,8 @@ package libc
 
 when ODIN_OS == "windows" {
 	foreign import libc "system:libucrt.lib"
+} else when ODIN_OS == "darwin" {
+	foreign import libc "system:System.framework"
 } else {
 	foreign import libc "system:c"
 }
@@ -33,7 +35,23 @@ when ODIN_OS == "linux" {
 	}
 
 	MB_CUR_MAX :: #force_inline proc() -> size_t {
-		return __ctype_get_mb_cur_max()
+		return size_t(__ctype_get_mb_cur_max())
+	}
+}
+
+
+when ODIN_OS == "darwin" {
+	RAND_MAX :: 0x7fffffff
+
+	// GLIBC and MUSL only
+	@(private="file")
+	@(default_calling_convention="c")
+	foreign libc {
+		___mb_cur_max :: proc() -> int ---
+	}
+
+	MB_CUR_MAX :: #force_inline proc() -> size_t {
+		return size_t(___mb_cur_max())
 	}
 }