[bazel] Fix one missed target also broken by ff844df (llvm#142854)

a4320ba fixed most targets but missed
one.

Author: rupprecht

utils/bazel/llvm-project-overlay/libc/BUILD.bazel

@@ -4341,6 +4341,7 @@ libc_function(
     hdrs = ["src/string/strncpy.h"],
     deps = [
         ":__support_common",
+        ":__support_macros_null_check",
     ],
 )