[libc][bazel] Fix BUILD.bazel after 5ff2774. (llvm#137404)

Add a missing dependency to __support_macros_null_check.

Author: vonosmas

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

@@ -1000,6 +1000,7 @@ libc_support_library(
         ":__support_cpp_bit",
         ":__support_cpp_type_traits",
         ":__support_macros_attributes",
+        ":__support_macros_null_check",
         ":__support_macros_optimization",
         ":__support_math_extras",
         ":llvm_libc_macros_stdfix_macros",