KVM: x86: Force KVM_WERROR if the global WERROR is enabled

Force KVM_WERROR if the global WERROR is enabled to avoid pestering the
user about a Kconfig that will ultimately be ignored.  Force KVM_WERROR
instead of making it mutually exclusive with WERROR to avoid generating a
.config builds KVM with -Werror, but has KVM_WERROR=n.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20240517180341.974251-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>