This reduces bootstrap cost for Windows customers, resolving the issue initially submitted as #12502 .

The `toolsrc` tree was extracted to https://github.com/microsoft/vcpkg-tool. `bootstrap.sh` was changed to download the right source tarball, extract, and build it. This was chosen over the previous attempt, a submodule, over concerns of accidentally destroying people's local modifications.

utilities.cmake: Disable warnings that are firing on Azure Pipelines CI machines due to different Clang version.

expected.h: Fix a bug I introduced in https://github.com/microsoft/vcpkg/pull/15638/ because I was under the impression expected worked like optional (in that value_or_exit for it should be treated as a program bug)

build.cpp: Add (void)s to silence warnings.

binarycaching.cpp: Repair assumption that the current directory is C: which isn't true on the Hosted Azure Pipelines agents.

others: Make unit tests respect %VCPKG_ROOT%, as necessary in the vcpkg_tool repo. Note that this required splitting vcpkgcmdarguments::ImbueFromEnvironment into the once-only process modifying part and the just imbue from environment part.

* initial openbsd support in vcpkg

* after clang-format

* hardcoded in the preferred compiler for openbsd in bootstrap scipt (thanks @tormfinn)

* Fetch a patched pkg-config because openbsd pkg-config lacks {fcfiledir}

* fixes from review feedback

* corrected hash for pkg-config.openbsd

* re-added missing endif()

* regenerate docs

* Update scripts/cmake/vcpkg_configure_meson.cmake

Co-authored-by: Nicole Mazzuca <mazzucan@outlook.com>

* Change to using more target-focused cmake

* Add vcpkg_target_add_warning_options

* targetify the rest

* move the globs together

* Force-include pch.h on non-windows

* Rename VCPKGLIB_NON_PCH_* to VCPKGLIB_* in globs

* Remove `include "pch.h"`s

* missed a few lines

* fix build

* fix CMAKE_CURRENT_SOURCE_DIR

* try to fix VCPKG_REQUIRE_LINK_CXXFS

* change msvc-stl logic

* fix build

* CR

* clang-format

* Apply suggestions from code review

Thanks @ras0219!

Co-authored-by: JackBoosY <yuzaiyang@beyondsoft.com>
Co-authored-by: ras0219 <533828+ras0219@users.noreply.github.com>

==== Changes Related to manifests ====

* Add the `manifests` feature flag
  * This only says whether we look for a `vcpkg.json` in the cwd, not
    whether we support parsing manifests (for ports, for example)
* Changes to the manifests RFC
  * `"authors"` -> `"maintainers"`
  * `--x-classic-mode` -> `-manifests` \in `vcpkg_feature_flags`
  * reserve `"core"` in addition to `"default"`, since that's already
    reserved for features
  * Add a small helper note about what identifiers must look like
  * `<license-string>`: SPDX v3.8 -> v3.9
  * `"feature"."description"` is allowed to be an array of strings as well
  * `"version"` -> `"version-string"` for forward-compat with versions
    RFC
* Add the `--feature-flags` option
* Add the ability to turn off feature flags via passing
  `-<feature-flag>` to `VCPKG_FEATURE_FLAGS` or `--feature-flags`
* Add CMake toolchain support for manifests
  * Requires either:
    * a feature flag of `manifests` in either `Env{VCPKG_FEATURE_FLAGS}`
      or `VCPKG_FEATURE_FLAGS`
    * Passing the `VCPKG_ENABLE_MANIFESTS` option
  * The toolchain will install your packages to
    `${VCPKG_MANIFEST_DIR}/vcpkg_installed`.
* Add MSBuild `vcpkg integrate install` support for manifests
  * Requires `VcpkgEnableManifest` to be true
* `vcpkg create` creates a port that has a `vcpkg.json` instead of a
  `CONTROL`
* argparse, abseil, 3fd, and avisynthplus ports switched to manifest
  from CONTROL
* Add support for `--x-manifest-root`, as well as code for finding it if
  not passed
* Add support for parsing manifests!
* Add a filesystem lock!

==== Important Changes which are somewhat unrelated to manifests ====

* Rename `logicexpression.{h,cpp}` to `platform-expression.{h,cpp}`
* Add `PlatformExpression` type which takes the place of the old logic
  expression
  * Split the parsing of platform expressions from checking whether
    they're true or not
  * Eagerly parse PlatformExpressions as opposed to leaving them as
    strings
* Add checking for feature flag consistency
  * i.e., if `-binarycaching` is passed, you shouldn't be passing
    `--binarysource`
* Add the `Json::Reader` type which, with the help of user-defined
  visitors, converts JSON to your internal type
* VcpkgArgParser: place the switch names into a constant as opposed to
  using magic constants
  * In general update the parsing code so that this ^ works
* Add `Port-Version` fields to CONTROL files
  * This replaces the existing practice of
    `Version: <my-version>-<port-version>`

==== Smaller changes ====
* small drive-by cleanups to some CMake
  * `${_VCPKG_INSTALLED_DIR}/${VCPKG_TARGET_TRIPLET}` ->
    `${CURRENT_INSTALLED_DIR}`
  * Remove `-analyze` when compiling with clang-cl, since that's not a
    supported flag (vcpkg's build system)
  * Add a message about which compiler is detected by vcpkg's build
    system machinery
* Fix `Expected::then`
* Convert `""` to `{}` for `std::string` and `fs::path`, to avoid a
  `strlen` (additionally, `.empty()` instead of `== ""`, and `.clear()`)
* Add `Strings::strto` which converts strings to numeric types
* Support built-in arrays and `StringView` for `Strings::join`
* Add `operator<` and friends to `StringView`
* Add `substr` to `StringView`
* SourceParagraphParser gets some new errors

The existing code did not correctly pass `CXX` to cmake.

There are quite a few changes to the CMake build system packaged up into
one set here:
* Added `toolsrc/cmake/utilities.cmake`, which contains the following:
  * `vcpkg_detect_compiler` -- get the name of the C++ compiler, as one
    of {gcc, clang, msvc}
  * `vcpkg_detect_standard_library` -- get the name of the standard
    library we're linking to, as one of {libstdc++, libc++, msvc-stl}
  * `vcpkg_detect_std_filesystem` -- figure out how to link and call
    into C++17's filesystem; whether one needs to link to `stdc++fs` or
    `c++fs`, and whether to use `<filesystem>` or
    `<experimental/filesystem>`.
* Added a `VCPKG_WARNINGS_AS_ERRORS`, split off from
  `VCPKG_DEVELOPMENT_WARNINGS`, which allows one to use the development
  warnings without passing -Werror
* Rename `DEFINE_DISABLE_METRICS` to `VCPKG_DISABLE_METRICS` -- the
  former will now print a deprecation message and set the latter.
* Now, print a deprecation message on `WERROR`; it doesn't do anything
  since the behavior it requested is now the default.
* Pass `-std=c++17` if the compiler allows it, instead of `-std=c++1z`
* Do some code movement
* Pass `USE_STD_FILESYSTEM` if possible, instead of only on minGW
  * Renamed to `VCPKG_USE_STD_FILESYSTEM`

Additionally, we now pass `/W4` in Debug mode on x86 in the Visual
Studio build system; this brings it in line with the CMake build system,
and the x64 Visual Studio build system.

And finally, we make some minor code changes to support compiling in
VCPKG_DEVELOPMENT_WARNINGS mode.