Set up for running tests on VMS.

* run_make_tests.pl: set $port_type to be 'VMS-DCL' when the test are
run from the VMS DCL Interpreter.  When the tests are run from GNV
on VMS, the $port_type will be 'UNIX'.
* run_make_tests.com: VMS search list support.  This is needed for
using a search list such as prj_root = lcl_root:,vms_root:,src_root:
for building and testing.
[SV 42447]: VMS simulate exporting symbols

This also includes fixing the most of the exit handling code for VMS.

Self tests:
 Previously about 94 Tests in 36 categories fail.
 Now about 45 tests in 22 categories fail.

Because some tests do not properly clean up, the number of tests that
fail can vary by one or two test cases between consecutive runs.

* Makefile.am: Add new VMS files.
* job.c: add prototype for vms_strsignal().
* job.c: (child_error): Remove VMS specific code as no longer needed.
* job.c: (reap_children): The VMS specific code was setting the
status to 0 instead of setting it to the proper exit status.
* job.h: Add vms_launch_status to struct child.
* main.c: (main): Use environment variables for options to use MCR
* instead of a foreign command, and to always use command files for
subprocesses.
For VMS use (set_program_name) routine which is common to ports of
other GNU packages to VMS to set the program name used internally.
Use (vms_putenv_symbol) to set up symbols to be visible in child
programs, including recursive make launched by execve()
Start of Bash shell detection code for VMS.
* makefile.com: Need nested_include=none for building on VMS search
lists.  Add vms_progname, vms_exit, and vms_export_symbol.
* makefile.vms: Need nested_include=none for building on VMS search
lists.  Add vms_progname, vms_exit, vms_export_symbol.
* makeint.h: Make sure non-standard "VMS" macro is defined.  Add
prototypes for new VMS routines.  Remove VMS-specific failure codes.
* vmsjobs.c: Add VMS POSIX exit code constants.
(_is_unixy_shell): Detect Bash shell.
(vms_strsignal): simulate strsignal() on VMS.
(vmsHandleChildTerm): fix to properly report failed LIB$SPAWN() exit
status codes.  Remove code that duplicated code in job.c.
(child_execute_job): Export environment symbols before spawning a
child and restore afterward unless option to use command files for
subprocesses is set.  Improve handling of UNIX null commands ":".
* vms_exit.c: Provides vms_exit() to detect if an exit code is UNIX
or VMS, and converts the UNIX code into a VMS exit code.
* vms_export_symbol.c: Routines to create DCL symbols that work like
shell aliases or exported shell symbols and clean them up on exit.
* vms_export_symbol_test.com: Unit test for vms_export_symbol.c
* vms_progname.c: New file: VMS specific replace for progname.c that
is used in some GNU projects.
[SV 41758]: Fix archive support for VMS.

Upated to match change to run_make_tests and some future fixes to
make on VMS.

* arscan.c: Use ANSI compatible pragmas instead of VAX C extensions.
* tests/scripts/features/archives: Fix tests to use VMS rules and
answers when running on VMS and using DCL as a shell.
* tests/scripts/features/vpath3: Fix epected answer on test when
run on VMS.
* tests/scripts/vms/library: (New) Test the VMS library rules that
are not tested by existing tests.
Update README.VMS and move news to the NEWS file

* NEWS: Merge in VMS history.
* README.VMS: Remove VMS history, document current behavior and
known issues.
Fix VMS implicit rules and UNIX paths.

This fixes VMS implicit rules and UNIX style pathname handling.
It also fixes some of the VMS style pathname handling, more work
there will be needed later.
TODO: There are other case insensitive platforms besides VMS.
We need to find out why there is extra VMS code for this.  This
indicates either the extra VMS code is not needed, or the case
insensitive support may not be complete on the other case
insensitive platforms.

* default.c: Add missing definitions to default_suffix_rules[] and
default_variables[].
TODO: As it is important that VMS DCL mode definitions must always
be a superset of UNIX definitions, a better way of maintaining the
VMS DCL mode definitions should be devised.
* dir.c (downcase_inplace): Add a reentrant downcase() routine.
Add future support for VMS 8.2+ _USE_STD_STAT macro which will
disable a lot of VMS specific code from compiling.
(dir_file_exists_p): vmsify filename only if directory name has VMS
directory delimiters.
(file_exists_p): Handle both VMS and UNIX directories.
(file_impossible): Handle both VMS and Unix directories.  Track
whether a VMS format path is needed for the return value.
* file.c (lookup_file): Check if vmsify is needed; handle UNIX paths.
* implicit.c (pattern_search): Enable UNIX paths.
* read.c (parse_file_seq): Enable UNIX paths.
* remake.c (f_mtime): Fix gpath_search call for VMS paths.
* rule.c (count_implicit_rule): Enable UNIX paths, Fix VMS paths.
* vpath.c (selective_vpath_search): Enable UNIX paths.
* tests/scripts/features/archives: [SV 43405] override AR variable.

Copyright-paperwork-exempt: yes
* main.c (main): [SV 43434] Handle NULL returns from ttyname().