Throughout, rename PROC_FORK1 to PROC_FORK.

Throughout, rename PROC_FORK1 to PROC_FORK.
* child_info.h: Rename PROC_* to _PROC_*.  Define PROC_* with additional
testing magic.  Eliminate old PROC_FORK and rename PROC_FORK1 to PROC_FORK.
* dcrt0.cc (_cygwin_testing_magic): New variable.  Added to magic number in
proc_info.
(alloc_stack): Eliminate old PROC_FORK test.
(dll_crt0_1): Ditto.  Use _PROC_* enums for test.  Subtract
_cygwin_testing_magic from child_proc_info->type so that normal cygwin programs
invoked by test suite programs do not consider themselves to be in a cygwin
environment.
(_dll_crt0): Ditto.  Move environment checks to initial_env function to
conserve on stack space.
(initial_env): New function.  Checks for testing and debugging environment
variables.
* init.cc (cygwin_hmodule): Move declaration.
* winsup.h: Declare variables used for cygwin testing.