[boost-modular-build-helper] Add self to host dependency

[JackBoosY]

Since the boost components all use the boost-modular-build.cmake installed in the host triplet, add itself to host triplet dependencies to avoid missing script issues when building with unofficial triplet:

Starting package 1/59: boost-context:arm-linux
Building package boost-context[core]:arm-linux...
-- Using community triplet arm-linux. This triplet configuration is not guaranteed to succeed.
-- [COMMUNITY] Loading triplet configuration from: /home/test/package/vcpkg/triplets/community/arm-linux.cmake
-- Using cached boostorg-context-boost-1.77.0.tar.gz.
-- Cleaning sources at /home/test/package/vcpkg/buildtrees/boost-context/src/ost-1.77.0-7a375ea06d.clean. Use --editable to skip cleaning for the packages you specify.
-- Extracting source /home/test/package/vcpkg/downloads/boostorg-context-boost-1.77.0.tar.gz
-- Using source at /home/test/package/vcpkg/buildtrees/boost-context/src/ost-1.77.0-7a375ea06d.clean
CMake Error at ports/boost-context/portfile.cmake:19 (include):
  include could not find requested file:

    /home/test/package/vcpkg/installed/x64-linux/share/boost-build/boost-modular-build.cmake
Call Stack (most recent call first):
  scripts/ports.cmake:142 (include)

Examples:

• boost-atomic
  

  vcpkg/ports/boost-atomic/portfile.cmake

  Line 22 in 3a68454

  include(${CURRENT_HOST_INSTALLED_DIR}/share/boost-build/boost-modular-build.cmake)

• boost-chrono
  

  vcpkg/ports/boost-chrono/portfile.cmake

  Line 14 in 3a68454

  include(${CURRENT_HOST_INSTALLED_DIR}/share/boost-build/boost-modular-build.cmake)

• boost-container
  https://github.com/microsoft/vcpkg/blob/master/ports/boost-container/portfile.cmake#L14

Related: #21740.

[dg0yt]

I don't understant this PR. The boost ports already have proper host dependencies on boost-modular-build-helper. This works for both native and cross builds. Verified with boost-context:x64-mingw-dynamic on linux.
The original problem may be an outdated installation of boost-modular-build-helper. We have seen such issues before, on windows (where cross build is a default configuration on x64 machines).

[JackBoosY]

@dg0yt I will confirm this with @PhoebeHui .

[Neumann-A]

Looks like a case for "supports": "native"?

[JackBoosY]

Robert already added this to each boost components in #16479.
I think it's not needed.