kbuild: fix CONFIG_CC_CAN_LINK(_STATIC) for cross-compilation with Clang

scripts/cc-can-link.sh tests if the compiler can link userspace
programs.

When $(CC) is GCC, it is checked against the target architecture
because the toolchain prefix is specified as a part of $(CC).

When $(CC) is Clang, it is checked against the host architecture
because --target option is missing.

Pass $(CLANG_FLAGS) to scripts/cc-can-link.sh to evaluate the link
capability for the target architecture.

Change-Id: I3e35aac919c15474dc560248a42fe5aeb5447bd5
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>