Don't install the xml syscall files which only contain Linux' syscalls.

--- gdb/Makefile.in.orig	Thu Sep  1 19:30:12 2011
+++ gdb/Makefile.in	Thu Sep  1 19:30:12 2011
@@ -1004,7 +1004,7 @@ install: all install-only 
 
 # The "install-only" target also installs the syscalls' XML files in
 # the system.
-install-only: $(CONFIG_INSTALL) xml-syscall-install
+install-only: $(CONFIG_INSTALL)
 	transformed_name=`t='$(program_transform_name)'; \
 			  echo gdb | sed -e "$$t"` ; \
 		if test "x$$transformed_name" = x; then \