Create a CMAKE_USE_SYSTEM_LIBRHASH option.

All clients of `cm_sha2` have been ported to `cmCryptoHash`, which now
uses librhash internally.

Fix `rhash_md5_final` to use unsigned integers for left shifting to
avoid the possibility of undefined overflow behavior.

We cannot fall back to the macro implementation because some call sites
may call it with an argument like `*ptr++` that has side effects.

When we install using the bundled librhash source, notify users of its
license terms.

Add '-w' or equivalent flag on compilers supporting it.
Tell MSVC to use its lowest warning level inside librhash sources.

Update `ustd.h` to include KWSys Large File Support configuration so
that consistent stream libraries are used (on AIX with XL).

Add a `cm_rhash.h` header to include the CMake-provided copy of the
`rhash.h` header from CMake sources.

We only need a subset of the hash algorithms supported by librhash.
Add preprocessor conditionals to remove source fragments that we do
not need.  Write an alternative algorithm enumeration that matches
the indexing on our reduced array.

Also remove a few fragments outright.

Alex Wang authored 8 years ago and Brad King committed 8 years ago

The clang-format pass in commit v3.6.0-rc1~54^2~1 (Revise C++ coding
style using clang-format, 2016-05-16) changed the template right angle
brackets from `>>` to `> >`, which defeats the purpose of this test.
Change it back and exclude this content from formatting.

On Linux the gzip tool is universally available, so our `.tar.gz` is
sufficient.

On macOS the gzip tool is universally available, so our `.tar.gz` is
sufficient.

The machine that builds the Linux binary has python 3 and 2.6, but the
latter is too old for the server mode test script.

Add the CMake_ENABLE_SERVER_MODE option explicitly to the configuration
of all binary builds.  We want to know the mode is available if the
build succeeds.

The 64-bit Windows binary is built in our second batch because it is
built on the same host as the 32-bit Windows binary.  When the
documentation generation was first added, it was not included in the
second batch because at the time that batch only included the Cygwin
binary.  Therefore the 64-bit Windows binary has been missing the
documentation since it was first created for CMake 3.6.

Since then the Cygwin binary was dropped so the second batch only
contains the 64-bit Windows binary.  Add the docs to it.

Closes: #16333

Per-source copyright/license notice headers that spell out copyright holder
names and years are hard to maintain and often out-of-date or plain wrong.
Precise contributor information is already maintained automatically by the
version control tool.  Ultimately it is the receiver of a file who is
responsible for determining its licensing status, and per-source notices are
merely a convenience.  Therefore it is simpler and more accurate for
each source to have a generic notice of the license name and references to
more detailed information on copyright holders and full license terms.

Our `Copyright.txt` file now contains a list of Contributors whose names
appeared source-level copyright notices.  It also references version control
history for more precise information.  Therefore we no longer need to spell
out the list of Contributors in each source file notice.

Replace CMake per-source copyright/license notice headers with a short
description of the license and links to `Copyright.txt` and online information
available from "https://cmake.org/licensing".  The online URL also handles
cases of modules being copied out of our source into other projects, so we
can drop our notices about replacing links with full license text.

Run the `Utilities/Scripts/filter-notices.bash` script to perform the majority
of the replacements mechanically.  Manually fix up shebang lines and trailing
newlines in a few files.  Manually update the notices in a few files that the
script does not handle.

Add a script to replace our previous per-source license notices with a
much simpler notice.  This will be used in a following commit and then
removed.

We do not actually run a check for this.

The test fails spuriously too often.  Additional work on the test
will be needed to make it more reliable.  For now just skip the
test when building nightly binaries so they can complete.

The toolchains we use to build on these platforms support it.

This will enable use of features such as ALIAS targets within CMake's
own build.

Cygwin has packaged CMake independently of upstream for a long time.
See its [cygport](https://github.com/cygwinports/cmake).

We include the `kvm.h` header on these platforms and call kvm APIs.
Link with the library to ensure they are available.

Roger Leigh authored 8 years ago and Brad King committed 8 years ago

Add it unconditionally.  It is present in FreeBSD 11, 10 and 9.

Backport curl upstream commit curl-7_50_2~32 (nss: refuse previously
loaded certificate from file, 2016-08-22).

This will allow build failure cases to be added later.

The Clang scan-build tool warns about assignments whose values are never
used, so initialize local variables at declaration instead.

Create a CMAKE_USE_SYSTEM_LIBUV option.

We only need the availability macros in `unix/internal.h`.  We already
include CoreServices where needed in implementation files.