tools/libxc: Fix build of 32bit toolstacks on CentOS 5.x following XSA-125

tools/libxc: Fix build of 32bit toolstacks on CentOS 5.x following XSA-125

gcc 4.1 of CentOS 5.x era does not like the typecheck in min() between
uint64_t and unsigned long.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
CC: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
CC: Ian Campbell <Ian.Campbell@citrix.com>
CC: Ian Jackson <Ian.Jackson@eu.citrix.com>
CC: Wei Liu <wei.liu2@citrix.com>
(cherry picked from commit 6c1cb3dba4ff97dd40909670755f24fcdf903012)
Conflicts:
	tools/libxc/xc_domain.c
Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>