This change modifies how CMAKE_RC_COMPILER is configured to improve
the out-of-box experience for developers using Clang on Windows.
The previous behavior was to require the user to explicitly specify
the resource compiler when CMake was called. The new behavior
is to automatically attempt to locate the MSVC rc binary and use that
if it's found. If rc is not available, CMake will now fall back to
Clang's llvm-rc binary.

With this change in place, trivial C/C++ programs can be generated
with Ninja and Clang on Windows without running into errors about
a missing resource compiler.

Fixes: #19318

a7a5f376 cmFileCommand: Use cmSubcommandTable
b66b7464 Introduce cmSubcommandTable
2b785875 cmFileCommand: turn into free function
9703c657 cmFileCommand: put subcommands in unnamed namespace
64f987c1 cmFileCommand: port to cmExecutionStatus
Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !3657

1a47d368 cmDefinitions: Cleanups and optimizations
Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !3666

ca292311 Autogen: Modernize to use cmStrCat for string concatenation
d02a99d9 Autogen: Modernize code to use cm::string_view for the info writer
Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !3663

2171f6ec Swift: correct SONAME flag for Darwin targets
Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !3640

e45187d5 FPHSA: Remove extra space in module components report
Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: Alex Turbov <i.zaufi@gmail.com>
Merge-request: !3655

5558070d cmExecutionStatus: Remove function Clear
Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !3654

In cmDefinitions:
- sort methods in source code by static or not static
- use `std::unordered_set<cm::string_view>` instead of `std::set<std::string>`
  for duplications tests.

18ce372e Help: Add 3.15.2 release notes
Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !3664

Merge-request: !3664

18b0330b clang-tidy: Enable performance-inefficient-string-concatenation
Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !3648

7ed84b1e FindPython: ensure virtual environments are correctly handled
Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !3649

959b97a2 Tests: testStringAlgorithms: Add cmTrimWhitespace, cmEscapeQuotes, cmTokenize
7fbcc16d cmStringAlgorithms: cmIsSpace, cmTrimWhitespace, cmEscapeQuotes, cmTokenize
Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !3647

8fe129e3 Help: Fix spelling typo in `CMAKE_MESSAGE_INDENT` docs
Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !3658

feeb0381 FindGLEW: Fix typo in verbose log message
ab822a9b FindGLEW: Add required OpenGL dependency in macOS
a8a3efa3 FindGLEW: Fix macOS library suffix selection
Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !3656

8ed86860 find_package: Fix prefer-config mode to not fail on missing optional package
Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !3653

493b8eae Help: Fix example output in the `CMAKE_MESSAGE_INDENT` documentation
Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !3651

d192caef CMakeDependentOption: Document that 4th parameter follows if-syntax
Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !3643

Merge-request: !3656

macOS requires OpenGL as INTERFACE_LINK_LIBRARIES dependency
in the GLEW targets. This commit fixes this issue.

Fix logic added by commit a7d85386 (FindGLEW: Update implementation,
2019-03-13, v3.15.0-rc1~375^2~1) on macOS.  macOS is recognized as both
UNIX and APPLE.  Consequently, the library suffix for shared and static
library was set, respectively, as `.so` and `.a`, just like UNIX systems.
Fix this by properly checking the OS type.

Fixes: #19542

Merge-request: !3653