Visual Studio always uses a complete NDK and not a standalone toolchain.
Let CMake handle the NDK and related logic correctly, avoid trying to
find the standalone toolchain version from the unified clang toolchain
in newer NDKs.

This allows us to skip `abi-*.cmake` in the next change.
In the future we may move all this information to the NDK.

This change adds hooks to key Android support files, so that NDK can
inject information or change cmake behaviors.

See https://github.com/codespell-project/codespell#readme

The following command was used:

```
codespell -q6 --skip="\
.git,\
*.json,\
./Copyright.txt,\
./Help/command/foreach.rst,\
./Help/prop_test/REQUIRED_FILES.rst,\
./Help/variable/CTEST_COVERAGE_COMMAND.rst,\
./Modules/CMakeCheckCompilerFlagCommonPatterns.cmake,\
./Modules/CMakeRCInformation.cmake,\
./Modules/Internal/CPack/NSIS.template.in,\
./Modules/FindMatlab.cmake,\
./Modules/MatlabTestsRedirect.cmake,\
./Modules/Platform/Windows-Clang.cmake,\
./Modules/Platform/Windows-Intel-Fortran.cmake,\
./Modules/Platform/Windows-MSVC.cmake,\
./Source/CMakeVersion.cmake,\
./Source/cmConvertMSBuildXMLToJSON.py,\
./Source/cmCreateTestSourceList.cxx,\
./Source/cmGlobalVisualStudio10Generator.cxx,\
./Source/cmExportBuildFileGenerator.cxx,\
./Source/cmExportInstallAndroidMKGenerator.cxx,\
./Source/cmExportInstallFileGenerator.cxx,\
./Source/cmExportSet.cxx,\
./Source/cmExportTryCompileFileGenerator.cxx,\
./Source/cmFindPackageCommand.cxx,\
./Source/cmInstallCommand.cxx,\
./Source/cmGeneratorExpressionLexer.cxx,\
./Source/cmLocalVisualStudio7Generator.cxx,\
./Source/cmOrderDirectories.cxx,\
./Source/cmTarget.cxx,\
./Source/kwsys/*,\
./Source/QtDialog/CMakeSetupDialog.ui,\
./Source/CPack/WiX/cmWIXRichTextFormatWriter.cxx,\
./Source/CTest/cmParseCoberturaCoverage.h,\
./Tests/CMakeTests/ImplicitLinkInfoTest.cmake.in,\
./Tests/RunCMake/CPack/tests/DMG_SLA/English.license.rtf,\
./Tests/RunCMake/CPack/tests/DMG_SLA/German.license.txt,\
./Tests/RunCMake/CPack/tests/DMG_SLA/German.menu.txt,\
./Tests/RunCMake/GoogleTest/xml_output.cpp,\
./Tests/RunCMake/Make/TargetMessages*,\
./Utilities/*,\
" \
-L "\
dependees,\
endwhile,\
fo,\
filetest,\
helpfull,\
nd,\
objext,\
stoll,\
supercedes,\
superceded,\
vas,\
varn,\
"
```

e3d3b7ddeb Android: Fix binutils selection with NDK r19+ unified toolchain

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !4318

In commit 97bca2f9fa (Android: Use unified toolchain in NDK r19+,
2019-07-26, v3.16.0-rc1~342^2) we hard-coded use of the unified
toolchain for NDK r19+ and skipped most of the old detection logic.
However, in that fast path we left out setting `_CMAKE_TOOLCHAIN_PREFIX`
for `CMakeFindBinutils` to select the matching binutils.  Add it.

Fixes: #20038

The CMake support for Android assumes cross-compilation using the NDK,
so stub out that Android NDK support and use the Linux support that's
already invoked. Set CMAKE_HOST_SYSTEM_NAME to "Android", rather than
"Linux".

Issue: #19840

The NDK build system now uses only a single toolchain in

    <ndk>/toolchains/llvm/prebuilt/<host>

Its compilers are always `bin/{clang,clang++}` and its binutils are
always `bin/<triple>-*`.  It is a standalone toolchain:

* The Anrdoid API level is specified at the end of `--target=`.
* The standard library may be specified via `-stdlib=`.
* No need to pass system includes or libraries explicitly.
* No need to pass `--sysroot` or `-gcc-toolchain`.

Teach CMake to recognize NDK versions that have a unified
toolchain with its own sysroot and use the above approach.

Fixes: #18739