3.5.x (RM #3472): Fix compilation on Solaris 11.

The DATA_TYPE_STRING enum value is defined in their zone.h file, but
we also use it in evaluation code, so compile these functions in a
separate file that doesn't include cf3.defs.h.

Fixes issue #3472.

Back-port of 5e24267e7d045ab7cf70b17dd3f927667d90476c for 3.5.3.
Conflicts resolved in:
	libpromises/Makefile.am
	libpromises/processes_select.c