x86, um: untangle uml ldt.h

* turn asm/ldt.h into ldt.h; update the (very few) users
* take host_ldt.h into sysdep, kill symlink mess
* includes of asm/arch/ldt.h turn into asm/ldt.h now

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
diff --git a/arch/um/Makefile b/arch/um/Makefile
index 33d59f1..909d16b 100644
--- a/arch/um/Makefile
+++ b/arch/um/Makefile
@@ -20,7 +20,7 @@
 
 # Have to precede the include because the included Makefiles reference them.
 SYMLINK_HEADERS := archparam.h system.h processor.h ptrace.h \
-	module.h vm-flags.h elf.h host_ldt.h
+	module.h vm-flags.h elf.h
 SYMLINK_HEADERS := $(foreach header,$(SYMLINK_HEADERS),$(ARCH_DIR)/include/asm/$(header))
 
 # XXX: The "os" symlink is only used by arch/um/include/os.h, which includes