Clean up the namespace in a number of standard headers.

Clean up the namespace in a number of standard headers.

* In most cases, instead of the full load of <sys/types.h>,
  include <machine/stdint.h> which defines the __-types that
  <monetary.h>, <pwd.h>, <search.h>, <strings.h> and <wordexp.h>
  only need.

* Additionally, extend the visibility of the size_t definition
  and adjust WRDE_NOSYS's visibility because it was only in the
  standard up to Issue 6.

* In <time.h>, include <sys/stdint.h> to get at __pid_t too.

* Likewise, include <sys/stdint.h> in <sys/wait.h> and provide
  a definition of pid_t as required.