Replace the members for the Makefile and the Error with a
cmExecutionStatus.  Re-implement GetMakefile and SetError based on that.

Both functions should be called directly on the cmExecutionStatus that is
passed to InitialPass.  This will help us make all Commands immutable and
remove the need for cloning.

An old workaround for `std::allocator_traits<>::value_type` lints from
IWYU on `std::vector<>` usage breaks IWYU's handling of `<memory>`.
Convert the workaround to use the same approach we already use for a
workaround of `std::__decay_and_strip<>::::__type` lints.  Then update
the `<memory>` inclusions to follow the now-correct IWYU lints.

Reduce the number of files relying on `cmake.h`.

Fix some warnings that are new since clang-tidy version 4, and update
`.clang-tidy` to suppress the rest.

Store both the as-written and lower-case command names and use
the latter to avoid case-insensitive string comparisons.

With this I obtain 2-6% speed increase (on Windows) for the configure
step with no significant changes in memory usage.  A case-insensitive
comparison is a lot slower than just calling `==` because the operator
will use things like memcmp, so prefer the latter.

The `cmSystemTools::LowerCase` function allocates a new string each time
it is called, so before this change we were allocating in:

* cmMakefile::Configure two times for each function
  (to look for `cmake_minimum_required` and `project`)
* cmMakefile::ExecuteCommand twice by function by calling
  cmState::GetCommand and copying the name

Now we are only allocating once by function instead of four.

Signed-off-by: Matthias Maennich <matthias@maennich.net>

Changes done via `clang-tidy` with some manual fine-tuning
for the variable naming and `auto` type deduction
where appropriate.

The setters are only used to set boolean values.  The values are never
reset individually.

Closes: #14335

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names and years are hard to maintain and often out-of-date or plain wrong.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.

Replace use of cmsys::auto_ptr with a CM_AUTO_PTR macro that maps to
our own implementation adopted from the KWSys auto_ptr implementation.
Later we may be able to map CM_AUTO_PTR to std::auto_ptr on compilers
that do not warn about it.

Automate the client site conversions:

    git grep -l auto_ptr -- Source/ | grep -v Source/kwsys/ | xargs sed -i \
      's|cmsys::auto_ptr|CM_AUTO_PTR|;s|cmsys/auto_ptr.hxx|cm_auto_ptr.hxx|'

Run the `Utilities/Scripts/clang-format.bash` script to update
all our C++ code to a new style defined by `.clang-format`.
Use `clang-format` version 3.8.

* If you reached this commit for a line in `git blame`, re-run the blame
  operation starting at the parent of this commit to see older history
  for the content.

* See the parent commit for instructions to rebase a change across this
  style transition commit.

Sort include directives within each block (separated by a blank line) in
lexicographic order (except to prioritize `sys/types.h` first).  First
run `clang-format` with the config file:

    ---
    SortIncludes: false
    ...

Commit the result temporarily.  Then run `clang-format` again with:

    ---
    SortIncludes: true
    IncludeCategories:
      - Regex:    'sys/types.h'
        Priority: -1
    ...

Commit the result temporarily.  Start a new branch and cherry-pick the
second commit.  Manually resolve conflicts to preserve indentation of
re-ordered includes.  This cleans up the include ordering without
changing any other style.

Use the following command to run `clang-format`:

    $ git ls-files -z -- \
        '*.c' '*.cc' '*.cpp' '*.cxx' '*.h' '*.hh' '*.hpp' '*.hxx' |
      egrep -z -v '(Lexer|Parser|ParserHelper)\.' |
      egrep -z -v '^Source/cm_sha2' |
      egrep -z -v '^Source/(kwsys|CursesDialog/form)/' |
      egrep -z -v '^Utilities/(KW|cm).*/' |
      egrep -z -v '^Tests/Module/GenerateExportHeader' |
      egrep -z -v '^Tests/RunCMake/CommandLine/cmake_depends/test_UTF-16LE.h' |
      xargs -0 clang-format -i

This selects source files that do not come from a third-party.
Inspired-by: Daniel Pfeifer <daniel@pfeifer-mail.de>

Each source file has a logical first include file.  Include it in an
isolated block so that tools that sort includes do not move them.

All it does is call cmListFileContext::FromCommandContext, so move this
to the call sites.

Commit v3.4.0-rc1~494^2~4 (cmMakefile: Add API for elseif to create
backtrace., 2015-05-29) removed the use of cmMakefileCall to push/pop
execution context in favor of a new way to create backtraces.

However, a call to cmMakefile::GetExecutionContext is still invoked to
issue a contextual CMP0054 warning through cmConditionEvaluator.  As
the elseif is not part of the call stack, this resulted in trying to
access an empty vector.

Avoid the attempt at getting execution context when evaluating elseif by
constructing a context and backtrace on behalf of the cmConditionEvaluator
in all cases.

Avoid copying many strings into each backtrace object.

There is no need to store the FilePath for every function, as it is
known by other means.

If it's known that it is an "if" it can't be an "elseif".

Inspired-by: Doug Barbieri
Signed-off-by: Gregor Jasny <gjasny@googlemail.com>