Commit 0a0e2ea6 ("ACPI: processor: Move MWAIT quirk out of
acpi_processor.c") moved the MWAIT quirk code into arch/x86 but left
calls to it in the ACPI PDC processor code that is shared with Itanium,
breaking the latter build.

Since the quirk is specific to a certain x86-based platform, stub out
the function acpi_proc_quirk_mwait_check() when building for ia64.

Fixes: 0a0e2ea6 ("ACPI: processor: Move MWAIT quirk out of acpi_processor.c")
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>