libc: fix typo in __RENAME macro

Apparently __strncpy_real redirects to strcpy instead of strncpy for GCC
builds. This is bad, and it confused a project compiled by GCC that uses

I audited all of the FORTIFY-related __RENAMEs both manually and with a
script I hacked together; they all look correct aside from this one.

FWIW, with the cleaned up clang FORTIFY, lots of the `void foo()
__RENAME(foo)` will just become `void foo()` if this last thing I'm
working on gets through review.

Bug: 35329524
Test: Previously broken project now seems to work. Bullhead and Ryu
both build + boot.

Change-Id: Ib18ee3535ae31eb7e8ae846dc012f9b64cac80bf
diff --git a/libc/include/string.h b/libc/include/string.h
index 6520996..c178a3c 100644
--- a/libc/include/string.h
+++ b/libc/include/string.h
@@ -412,7 +412,7 @@
 #undef __error_zero_size
 #undef __error_if_overflows_dst
 #else // defined(__clang__)
-extern char* __strncpy_real(char* __restrict, const char*, size_t) __RENAME(strcpy);
+extern char* __strncpy_real(char* __restrict, const char*, size_t) __RENAME(strncpy);
 extern void* __memrchr_real(const void*, int, size_t) __RENAME(memrchr);
 extern size_t __strlcpy_real(char* __restrict, const char* __restrict, size_t)