Toolset update: VS 2019 16.10 Preview 1

[StephanTLavavej]

• stl/msbuild/stl_base/stl.files.settings.targets: Our internal legacy build system can build ppltasks.cpp with /permissive- now.
  • The modern CMake build system doesn't need this change:

    STL/stl/CMakeLists.txt

    Lines 288 to 290 in 108a112

    	${CMAKE_CURRENT_LIST_DIR}/src/mutex.cpp
    	${CMAKE_CURRENT_LIST_DIR}/src/pplerror.cpp
    	${CMAKE_CURRENT_LIST_DIR}/src/ppltasks.cpp

• Update the Virtual Machine Scale Set.
  • README.md: Mention VS 2019 16.10 Preview 1 and Python 3.9.2 as dependencies.
  • azure-devops/create-vmss.ps1: Move back to westus2 (after Azure Pipelines: Move VMSS location, don't publish artifacts #1654) and try switching from Standard_D32as_v4 to Standard_D32ds_v4. This should have comparable performance, and spot VMs are approximately half the cost.
  • azure-devops/provision-image.ps1: Update to PowerShell 7.1.2 and Python 3.9.2.
  • azure-pipelines.yml: Use the new pool.
• stl/inc/yvals_core.h: Increase required _MSC_VER to 1929.
  • Note that VS 2019 16.8 and 16.9 shared 1928, while 16.10 and 16.11 will share 1929.
  • The internal "checked-in toolset" has already been updated.
• stl/inc/xatomic.h: Remove an _mm_pause declaration workaround.
• stl/inc/type_traits: Fix <type_traits>: Remove _IS_LAYOUT_COMPATIBLE_SUPPORTED macro and related __builtin*() intrinsics #1637 by removing the _IS_LAYOUT_COMPATIBLE_SUPPORTED checks; now we unconditionally use the new names.
• Remove workarounds for VSO-1271718, DevCom-1318357/VSO-1270432, DevCom-1318341/VSO-1269894, VSO-1275530, DevCom-1333853/VSO-1276453, DevCom-1336816/VSO-1277619, DevCom-1336819/VSO-1277640, and an unspecified bug that was fixed in 16.10 Preview 1.
• tests/std/tests/P0218R1_filesystem/test.cpp: Remove an outdated comment about "not a PM_ constant"; that machinery was removed long ago.
• tests/std/tests/Dev11_0836436_get_time/test.cpp: Fix/add [locale.time.get.members] citations, noticed after merging <iomanip>: get_time handles leading zeros incorrectly #1620.
• .gitattributes: Mark *.h as C++ (they're being detected as C) and *.cfg as Python (they're being detected as HAProxy, whatever that is).
• Update the vcpkg submodule for Boost 1.75.0.
  • CMakeLists.txt: Require Boost 1.75.0.

[MahmoudGSaleh]

LGTM

[StephanTLavavej]

I reverted the /headerUnit:angle change, as it was causing the mysterious ICEs, and reverted those workaround additions (leaving only workaround removals in the test). Reported internally as VSO-1287925 "/headerUnit:angle ICEs".