Add additional search paths for SDL on MSVC

This fixes issue 14029. Thanks to Paul "TBBle" Hampson for reporting the issue
and a fix proposal.
cmake-gui: Configure again if a variable is changed before Generate is pushed.
Merge topic 'qt-dialog-reconfigure' into next

b566987 cmake-gui: Configure again if a variable is changed before Generate is pushed.
CMake Nightly Date Stamp
Don't unintentionally match AppleClang.

Only run the msvcxx_sealed test for MSVC, not for Clang.
Merge topic 'target_compile_features' into next

c40fe09 Don't unintentionally match AppleClang.
Record standard of features, if applicable.
Merge topic 'target_compile_features' into next

5d09f14 Record standard of features, if applicable.
Clean up test.
Merge topic 'cross-compiling-toolchain-variables' into next

6b7e19e Clean up test.
Record the compilers capable of the cxx_delegating_constructors feature.

Add a feature test using the compiler macros and the preprocessor to
determine available features. Add a unit test which outputs the
feature test file compiled. Record the list of features in
the SystemInformation unit test.

Add a CMAKE_CXX_COMPILE_FEATURES variable which contains all features
known to the loaded compiler, and a CMAKE_CXX_KNOWN_FEATURES variable
containing all features known to CMake. Add language standard specific
variables for internal use to determine the standard-specific compile
flags to use. Add internal variables matching CMAKE_PP_NAME_<feature>
for each feature. Those variables are used as preprocessor defines.
Record compilers capable of the gnuxx_typeof feature.
Record compilers capable of msvcxx_sealed feature.

Clang-cl is capable of this feature, but that is not yet released,
nor have I tested it.
Add target_compile_features command.

This can be used to set the compiler features required by particular
targets. An error is issued at CMake time if the compiler does not
support the required feature. If a language dialect flag is required
by the features used, that will be added automatically.
cmTarget: Make COMPILE_FEATURES available as a target property.
cmTarget: Allow populating COMPILE_FEATURES using generator expressions.
cmTarget: Transitively evaluate compiler features.

Extend the interface of the target_compile_features command with
PUBLIC and INTERFACE keywords. Populate the INTERFACE_COMPILER_FEATURES
target property if they are set. Consume the INTERFACE_COMPILER_FEATURES
target property from linked dependent targets to determine the final
required compiler features and the compile flag, if needed.
cmTargetPropCommandBase: Change the interface to return bool.

This is needed for the target_compile_features command, which
may fail at configure time if an invalid feature is specified.
Base the target_compile_features command on cmTargetPropCommandBase.

This gives us 'free' handling of IMPORTED, ALIAS, INTERFACE,
non-compilable and missing targets.
Introduce CMAKE_STAGING_PREFIX variable.

This variable can be useful in cross-compiling contexts where the
sysroot is read-only or where the sysroot should otherwise remain
pristine.

If the new CMAKE_STAGING_PREFIX variable is set, it is used instead
of CMAKE_INSTALL_PREFIX when generating the installation rules in
cmake_install.cmake.

This way, the CMAKE_INSTALL_PREFIX variable
always refers to the installation prefix on the target device, regardless
of whether host==target.

If any -rpath paths passed to the linker contain the CMAKE_STAGING_PREFIX,
the matching path fragments are replaced with the CMAKE_INSTALL_PREFIX.
Matching paths in the -rpath-link are not transformed.

The cross-prefix usr-move workaround is assumed not to require extension
regarding CMAKE_STAGING_PREFIX. The staging area is a single prefix, so
there is no scope for cross-prefix symlinks. The CMAKE_INSTALL_PREFIX
is still used to determine the workaround path, and that variable
remains the relevant one even if CMAKE_STAGING_PREFIX is used. If the
generated export files are deployed to the target, the workaround
will still be in place, and still be employed if required.