work around busted capability.h

work around busted capability.h

It contains things like:
  #ifndef _LINUX_TYPES_H
  #define _LINUX_TYPES_H
  #include <stdint.h>
  typedef uint32_t __u32;
  typedef __u32 __le32;
  ...

which result in:
  /usr/include/asm-generic/int-ll64.h:30:42: error: conflicting types for ‘__u64’
  /usr/include/sys/capability.h:39:18: note: previous declaration of ‘__u64’ was here
  make[1]: *** [src/libsystemd_core_la-unit.lo] Error 1
  make[1]: Leaving directory `/home/kay/work/src/systemd'
  make: *** [all] Error 2

So, include linux/types.h to get around that.