um: set __HAVE_ARCH_GATE_AREA for x86_64

Implement arch_vma_name() and make get_gate_vma(), in_gate_area() and
in_gate_area_no_mm() a nop.

We need arch_vma_name() to support vDSO.

Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/um/sys-x86_64/mem.c b/arch/um/sys-x86_64/mem.c
new file mode 100644
index 0000000..5465187
--- /dev/null
+++ b/arch/um/sys-x86_64/mem.c
@@ -0,0 +1,26 @@
+#include "linux/mm.h"
+#include "asm/page.h"
+#include "asm/mman.h"
+
+const char *arch_vma_name(struct vm_area_struct *vma)
+{
+	if (vma->vm_mm && vma->vm_start == um_vdso_addr)
+		return "[vdso]";
+
+	return NULL;
+}
+
+struct vm_area_struct *get_gate_vma(struct mm_struct *mm)
+{
+	return NULL;
+}
+
+int in_gate_area(struct mm_struct *mm, unsigned long addr)
+{
+	return 0;
+}
+
+int in_gate_area_no_mm(unsigned long addr)
+{
+	return 0;
+}