Support building in specific modes without a custom triplet.

[teo-tsirpanis]

This PR introduces the VCPKG_DEFAULT_BUILD_TYPE option in the CMake toolchain file, that provides a default value to VCPKG_BUILD_TYPE when building the ports.

Besides debug or release, this option can also be set to auto. In that case, vcpkg will consider the CMAKE_BUILD_TYPE or CMAKE_CONFIGURATION_TYPES variables, and if all configurations are known (Debug, Release, RelWithDebInfo, MinSizeRel) and map to only debug or release, it will build the ports in only that mode. If VCPKG_DEFAULT_BUILD_TYPE is not specified, or the CMake project is being built in an unknown configuration, the existing behavior is preserved and vcpkg will default to building in both modes.

Let's talk about how it works. When VCPKG_DEFAULT_BUILD_TYPE is specified, its value (after resolving auto) will be passed to the vcpkg tool via the --x-build-type setting, introduced in microsoft/vcpkg-tool#1231. The tool will propagate VCPKG_DEFAULT_BUILD_TYPE when running the portfile in script mode, and ports.cmake will default VCPKG_BUILD_TYPE to VCPKG_DEFAULT_BUILD_TYPE if the latter is specified. This will happen before the triplet file gets included, to allow the triplet to override the build type and maintain compatibility.

VCPKG_DEFAULT_BUILD_TYPE is supported only in manifest mode.

Fixes #10683

Depends on microsoft/vcpkg-tool#1231

[Neumann-A]

Does not fix #1626. The original issue was about adding subdirs for release/debug. But that issue can probably be closed as not planned.

[Neumann-A]

This logic is mostly unnecessary.

The cases are:
Multi Config Generator -> You want both or an override to only use release libs (!windows)
Single Config Generator -> You want one depending on CMAKE_BUILD_TYPE or an override to use release in debug builds. (!windows)

[teo-tsirpanis]

Does not fix #1626.

Thanks, updated to point to #10683 (which is closed with an ask to reopen at the bottom).

[LilyWangLL]

Convert this PR to draft since there is no progress. Please ping us if this PR is ready for review again.

[dg0yt]

Rebuilding the whole world in CI. Maybe it should be limited to a single triplet for a first discussion.

[teo-tsirpanis]

Oops, I updated the branch as a matter of routine. 😟

Can someone with permissions please cancel CI? Thanks and sorry for any disruption.

[dg0yt]

Can someone with permissions please cancel CI? Thanks and sorry for any disruption.

Push something like bff8a33

[teo-tsirpanis]

Thanks!