Tests: Drop kwsys test

KWSys now has its own dashboard and test clients that run on all the
machines where we test CMake.  We no longer need a test inside CMake to
test KWSys independently.
Tests: Drop CMAKE_TEST_GENERATOR and CMAKE_TEST_MAKEPROGRAM options

Drop the option to test with a different generator and make program than
was used to build.  This was used only to test support for the Open
Watcom compiler which at one time could not build CMake.  Instead we
will allow CMake to be configured to skip building binaries and just run
the test suite using an external CMake (in a future change).

For now leave the two option variables hard-coded to the old option
defaults until code can be updated to stop using them.
Tests: Drop CMAKE_TEST_MSVC and test MSVC directly

Now that we no longer support running tests using a different generator
we can trust the MSVC platform indicator directly.
Tests: Rename CMAKE_TEST_DEVENV -> CMake_TEST_DEVENV

Follow the convention of naming variables related to the CMake build
itself as "CMake_" rather than "CMAKE_".  While at it, consolidate the
code computing CMake_TEST_DEVENV to be more localized.
Tests: Rename CMAKE_TEST_MAKEPROGRAM uses for nested test projects

In the ExportImport, Fortran, and MacRuntimePath tests the
CMAKE_TEST_MAKEPROGRAM variable is used to pass an explicit request for
a CMAKE_MAKE_PROGRAM value to be used when building the inner projects.
Rename these use cases to CMake_TEST_NESTED_MAKE_PROGRAM.
Tests: Rename CMAKE_TEST_MAKEPROGRAM uses for explicit make program

Rename uses of the variable for specifying the make program used to
build test projects to CMake_TEST_EXPLICIT_MAKE_PROGRAM.
Tests: Drop CMAKE_TEST_MAKEPROGRAM variable

Remaining uses of the variable simply test its value so use
CMAKE_MAKE_PROGRAM directly instead.
Tests: Drop CMAKE_TEST_GENERATOR(|_TOOLSET) variables

s/CMAKE_TEST_GENERATOR/CMAKE_GENERATOR/g
Tests: Optionally configure tests exclusively, with an external CMake

Add an undocumented CMake_TEST_EXTERNAL_CMAKE option to name an external
CMake 'bin' directory.  Skip all main CMake binary builds and instead
configure the Tests directory to run using the external CMake provided.
This will provide a means to exercise the CMake test suite generating
for target platforms and compilers with which the CMake source does not
build.  That will allow us to raise the level of C++ features required
of a compiler to build our source while retaining tests for generating
projects with older compiler tools.
Revert topic 'alt-test-generator'

It will be replaced by a different approach.
Merge topic 'alt-test-generator' into next

3566b02e Revert topic 'alt-test-generator'
Merge topic 'test-external-cmake' into next

9608ef6f Tests: Optionally configure tests exclusively, with an external CMake
9f5bd180 Tests: Drop CMAKE_TEST_GENERATOR(|_TOOLSET) variables
76477267 Tests: Drop CMAKE_TEST_MAKEPROGRAM variable
a8a9fb7e Tests: Rename CMAKE_TEST_MAKEPROGRAM uses for explicit make program
40475573 Tests: Rename CMAKE_TEST_MAKEPROGRAM uses for nested test projects
f99734b2 Tests: Rename CMAKE_TEST_DEVENV -> CMake_TEST_DEVENV
3c01ee5a Tests: Drop CMAKE_TEST_MSVC and test MSVC directly
daf0a5fe Tests: Drop CMAKE_TEST_GENERATOR and CMAKE_TEST_MAKEPROGRAM options
e5096312 Tests: Drop kwsys test