WebEngine not building (missing pthread.h)

ninja: Entering directory `C:/qtb/bld/qtwebengine/gn/Release'
ninja: no work to do.
[1/2] Install the project...
-- Install configuration: "Release"
-- Installing: C:/qtb/bld/qtwebengine/install/bin/gn.exe
[11935/11939] Performing configure step for 'qtwebengine'
-- The CXX compiler identification is MSVC 19.29.30133.0
-- The C compiler identification is MSVC 19.29.30133.0
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: C:/Program Files (x86)/Microsoft Visual Studio/2019/Community/VC/Tools/MSVC/14.29.30133/bin/Hostx64/x64/cl.exe - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: C:/Program Files (x86)/Microsoft Visual Studio/2019/Community/VC/Tools/MSVC/14.29.30133/bin/Hostx64/x64/cl.exe - skipped
-- Detecting C compile features
-- Detecting C compile features - done
CMake Error at C:/qtb/bld/qtbase/lib/cmake/Qt6/Qt6Config.cmake:37 (include):
  include could not find requested file:

    C:/qtb/bld/qtbase/lib/cmake/Qt6/Qt6Targets.cmake
Call Stack (most recent call first):
  CMakeLists.txt:23 (find_package)


CMake Error at C:/qtb/bld/qtbase/lib/cmake/Qt6/Qt6Config.cmake:39 (include):
  include could not find requested file:

    C:/qtb/bld/qtbase/lib/cmake/Qt6/Qt6VersionlessTargets.cmake
Call Stack (most recent call first):
  CMakeLists.txt:23 (find_package)


-- Looking for pthread.h
-- Looking for pthread.h - not found
-- Found Threads: TRUE
CMake Error at C:/qtb/bld/qtbase/lib/cmake/Qt6/Qt6Config.cmake:37 (include):
  include could not find requested file:

    C:/qtb/bld/qtbase/lib/cmake/Qt6/Qt6Targets.cmake
Call Stack (most recent call first):
  C:/Program Files (x86)/Microsoft Visual Studio/2019/Community/Common7/IDE/CommonExtensions/Microsoft/CMake/CMake/share/cmake-3.20/Modules/CMakeFindDependencyMacro.cmake:47 (find_package)
  C:/qtb/bld/qtbase/lib/cmake/Qt6Core/Qt6CoreDependencies.cmake:8 (find_dependency)
  C:/qtb/bld/qtbase/lib/cmake/Qt6Core/Qt6CoreConfig.cmake:40 (include)
  C:/qtb/bld/qtbase/lib/cmake/Qt6/Qt6Config.cmake:127 (find_package)
  CMakeLists.txt:23 (find_package)


CMake Error at C:/qtb/bld/qtbase/lib/cmake/Qt6/Qt6Config.cmake:39 (include):
  include could not find requested file:

    C:/qtb/bld/qtbase/lib/cmake/Qt6/Qt6VersionlessTargets.cmake
Call Stack (most recent call first):
  C:/Program Files (x86)/Microsoft Visual Studio/2019/Community/Common7/IDE/CommonExtensions/Microsoft/CMake/CMake/share/cmake-3.20/Modules/CMakeFindDependencyMacro.cmake:47 (find_package)
  C:/qtb/bld/qtbase/lib/cmake/Qt6Core/Qt6CoreDependencies.cmake:8 (find_dependency)
  C:/qtb/bld/qtbase/lib/cmake/Qt6Core/Qt6CoreConfig.cmake:40 (include)
  C:/qtb/bld/qtbase/lib/cmake/Qt6/Qt6Config.cmake:127 (find_package)
  CMakeLists.txt:23 (find_package)


CMake Error: The source directory "C:/qtb/bld/qtbase/lib/cmake/Qt6/config.tests/static_link_order" does not exist.
Specify --help for usage, or press the help button on the CMake GUI.
CMake Error at C:/qtb/bld/qtbase/lib/cmake/Qt6/QtPublicTargetHelpers.cmake:36 (try_compile):
  Failed to configure test project build system.
Call Stack (most recent call first):
  C:/qtb/bld/qtbase/lib/cmake/Qt6/QtPublicTargetHelpers.cmake:78 (__qt_internal_static_link_order_public_test)
  C:/qtb/bld/qtbase/lib/cmake/Qt6/Qt6Config.cmake:185 (__qt_internal_check_link_order_matters)
  C:/Program Files (x86)/Microsoft Visual Studio/2019/Community/Common7/IDE/CommonExtensions/Microsoft/CMake/CMake/share/cmake-3.20/Modules/CMakeFindDependencyMacro.cmake:47 (find_package)
  C:/qtb/bld/qtbase/lib/cmake/Qt6Core/Qt6CoreDependencies.cmake:8 (find_dependency)
  C:/qtb/bld/qtbase/lib/cmake/Qt6Core/Qt6CoreConfig.cmake:40 (include)
  C:/qtb/bld/qtbase/lib/cmake/Qt6/Qt6Config.cmake:127 (find_package)
  CMakeLists.txt:23 (find_package)


CMake Warning at C:/qtb/bld/qtbase/lib/cmake/Qt6/Qt6Config.cmake:127 (find_package):
  Found package configuration file:

    C:/qtb/bld/qtbase/lib/cmake/Qt6Core/Qt6CoreConfig.cmake

  but it set Qt6Core_FOUND to FALSE so package "Qt6Core" is considered to be
  NOT FOUND.
Call Stack (most recent call first):
  CMakeLists.txt:23 (find_package)


-- Configuring incomplete, errors occurred!
See also "C:/qtb/bld/qtwebengine/src/CMakeFiles/CMakeOutput.log".
See also "C:/qtb/bld/qtwebengine/src/CMakeFiles/CMakeError.log".
FAILED: qtwebengine/libs/src/qtwebengine-stamp/Release/qtwebengine-configure