Fixes a test suite failure.

Taken from: https://git.simple-cc.org/scc/commit/ee1f4c0fce40cf6436b63450a36bbe6b5b582844.html

diff --git a/tests/libc/execute/0043-wcsrtombs.c b/tests/libc/execute/0043-wcsrtombs.c
index 3de058c6..e691acac 100644
--- a/tests/libc/execute/0043-wcsrtombs.c
+++ b/tests/libc/execute/0043-wcsrtombs.c
@@ -54,7 +54,7 @@ static void
 tests_wcsrtombs(void)
 {
 	size_t r;
-	wchar_t *wc;
+	const wchar_t *wc;
 	mbstate_t st;
 	struct wcstests *tp;