xen: Use __has_include() in xen/percpu.h

Only x86 has an asm/percpu.h.  Have the compiler only include it if it's
present, rather than symlinking an empty file.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Michal Orzel <michal.orzel@amd.com>

xen/arch/arm/include/asm/Makefile

@@ -5,7 +5,6 @@ generic-y += hardirq.h
 generic-y += iocap.h
 generic-y += irq-dt.h
 generic-y += paging.h
-generic-y += percpu.h
 generic-y += random.h
 generic-y += softirq.h
 generic-y += vm_event.h

xen/arch/ppc/include/asm/Makefile

@@ -6,7 +6,6 @@ generic-y += hardirq.h
 generic-y += hypercall.h
 generic-y += iocap.h
 generic-y += paging.h
-generic-y += percpu.h
 generic-y += perfc_defn.h
 generic-y += random.h
 generic-y += softirq.h

xen/arch/riscv/include/asm/Makefile

@@ -6,7 +6,6 @@ generic-y += hardirq.h
 generic-y += hypercall.h
 generic-y += iocap.h
 generic-y += irq-dt.h
-generic-y += percpu.h
 generic-y += random.h
 generic-y += softirq.h
 generic-y += vm_event.h

xen/include/asm-generic/percpu.h

@@ -1,14 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-only */
-#ifndef __ASM_GENERIC_PERCPU_H__
-#define __ASM_GENERIC_PERCPU_H__
-
-#endif /* __ASM_GENERIC_PERCPU_H__ */
-
-/*
- * Local variables:
- * mode: C
- * c-file-style: "BSD"
- * c-basic-offset: 4
- * indent-tabs-mode: nil
- * End:
- */

xen/include/xen/percpu.h

@@ -27,7 +27,9 @@
 
 #define get_per_cpu_var(var)  (per_cpu__##var)
 
-#include <asm/percpu.h>
+#if __has_include(<asm/percpu.h>)
+# include <asm/percpu.h>
+#endif
 
 #ifndef __ASSEMBLER__