Googletest does not compile with POSIX Threads for Windows

**Describe the bug**

**pthreads4w** is installed and working. I can compile programs with it. If I build googletest with default settings it does not detect pthread. **pthreads4w** can only be compiled with Generator "NMake Makefiles". If I try to also compile googletest with that Generator build fails with a bunch of error messages.

I expect that configuration and build of googletest detect third party pthread installation on Microsoft Windows and successful compile it with default Generator "Visual Studio *" and with Generator "NMake Makefiles" and then use POSIX threads.

**Steps to reproduce the bug**

First [Install third party POSIX Threads for Windows](https://stackoverflow.com/q/69275376/5014688). Then configure googletest with default settings using PowerShell:

PS> cmake -S . -B build
-- Building for: Visual Studio 16 2019
-- Selecting Windows SDK version 10.0.19041.0 to target Windows 10.0.19042.
-- The C compiler identification is MSVC 19.28.29915.0
-- The CXX compiler identification is MSVC 19.28.29915.0
-- 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/14.28.29910/bin/Hostx64/x64/cl.exe - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- 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/14.28.29910/bin/Hostx64/x64/cl.exe - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Found Python: C:/Users/ingo/AppData/Local/Programs/Python/Python39/python.exe (found version "3.9.7") found components: Interpreter
-- Looking for pthread.h
-- Looking for pthread.h - found
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Failed
-- Looking for pthread_create in pthreads
-- Looking for pthread_create in pthreads - not found
-- Looking for pthread_create in pthread
-- Looking for pthread_create in pthread - not found
-- Check if compiler accepts -pthread
-- Check if compiler accepts -pthread - no
-- Found Threads: TRUE
-- Configuring done
-- Generating done
-- Build files have been written to: C:/Users/ingo/devel/googletest/build

As shown header files are found but **pthread** isn't detected. Following build of googletest works but without multithreading. If Configuring with Generator "NMake Makefiles" I get:

PS> rm -R build
PS> cmake -S . -B build -G "NMake Makefiles"
-- The C compiler identification is MSVC 19.28.29915.0
-- The CXX compiler identification is MSVC 19.28.29915.0
-- 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/14.28.29910/bin/Hostx64/x64/cl.exe - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- 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/14.28.29910/bin/Hostx64/x64/cl.exe - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Found Python: C:/Users/ingo/AppData/Local/Programs/Python/Python39/python.exe (found version "3.9.7") found components: Interpreter
-- Looking for pthread.h
-- Looking for pthread.h - found
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Failed
-- Looking for pthread_create in pthreads
-- Looking for pthread_create in pthreads - not found
-- Looking for pthread_create in pthread
-- Looking for pthread_create in pthread - found
-- Found Threads: TRUE
-- Configuring done
-- Generating done
-- Build files have been written to: C:/Users/ingo/devel/googletest/build

Looks good so far. But with building I get:

PS> cmake --build build
Scanning dependencies of target gmock_main
[ 9%] Building CXX object googlemock/CMakeFiles/gmock_main.dir/__/googletest/src/gtest-all.cc.objgtest-all.cc
C:\Users\ingo\devel\googletest\googletest\include\gtest/internal/gtest-port.h(1173): error C3861: 'nanosleep': identifier not found
C:\Users\ingo\devel\googletest\googletest\include\gtest/internal/gtest-port.h(1488): error C2011: 'testing::internal::ThreadWithParamBase': 'class' type redefinition
C:\Users\ingo\devel\googletest\googletest\include\gtest/internal/gtest-port.h(1287): note: see declaration of 'testing::internal::ThreadWithParamBase'
C:\Users\ingo\devel\googletest\googletest\include\gtest/internal/gtest-port.h(1537): error C2953: 'testing::internal::ThreadWithParam': class template has already been defined
C:\Users\ingo\devel\googletest\googletest\include\gtest/internal/gtest-port.h(1508): note: see declaration of 'testing::internal::ThreadWithParam'
C:\Users\ingo\devel\googletest\googletest\src/gtest-death-test.cc(671): error C3646: 'write_handle_': unknown override specifier
C:\Users\ingo\devel\googletest\googletest\src/gtest-death-test.cc(671): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
C:\Users\ingo\devel\googletest\googletest\src/gtest-death-test.cc(673): error C3646: 'child_handle_': unknown override specifier
C:\Users\ingo\devel\googletest\googletest\src/gtest-death-test.cc(673): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
C:\Users\ingo\devel\googletest\googletest\src/gtest-death-test.cc(678): error C3646: 'event_handle_': unknown override specifier
C:\Users\ingo\devel\googletest\googletest\src/gtest-death-test.cc(678): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
C:\Users\ingo\devel\googletest\googletest\src/gtest-death-test.cc(690): error C2065: 'child_handle_': undeclared identifier
C:\Users\ingo\devel\googletest\googletest\src/gtest-death-test.cc(690): error C2065: 'event_handle_': undeclared identifier
C:\Users\ingo\devel\googletest\googletest\src/gtest-death-test.cc(704): error C2065: 'write_handle_': undeclared identifier
C:\Users\ingo\devel\googletest\googletest\src/gtest-death-test.cc(705): error C2065: 'event_handle_': undeclared identifier
C:\Users\ingo\devel\googletest\googletest\src/gtest-death-test.cc(713): error C2065: 'child_handle_': undeclared identifier
C:\Users\ingo\devel\googletest\googletest\src/gtest-death-test.cc(717): error C2065: 'child_handle_': undeclared identifier
C:\Users\ingo\devel\googletest\googletest\src/gtest-death-test.cc(719): error C2065: 'child_handle_': undeclared identifier
C:\Users\ingo\devel\googletest\googletest\src/gtest-death-test.cc(754): error C2065: 'write_handle_': undeclared identifier
C:\Users\ingo\devel\googletest\googletest\src/gtest-death-test.cc(755): error C2065: 'event_handle_': undeclared identifier
C:\Users\ingo\devel\googletest\googletest\src/gtest-death-test.cc(760): error C2065: 'event_handle_': undeclared identifier
C:\Users\ingo\devel\googletest\googletest\src/gtest-death-test.cc(773): error C2065: 'event_handle_': undeclared identifier
C:\Users\ingo\devel\googletest\googletest\src/gtest-death-test.cc(773): error C2672: 'testing::internal::StreamableToString': no matching overloaded function found
--- snip ---
----snap ---
NMAKE : fatal error U1077: 'C:\PROGRA~2\MICROS~2\2019\COMMUN~1\VC\Tools\MSVC\1428~1.299\bin\Hostx64\x64\cl.exe' : return code '0x2'
Stop.
NMAKE : fatal error U1077: '"C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.28.29910\bin\HostX64\x64\nmake.exe"' : return code '0x2'
Stop.
NMAKE : fatal error U1077: '"C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.28.29910\bin\HostX64\x64\nmake.exe"' : return code '0x2'
Stop.

**Does the bug persist in the most recent commit?**
Yes.

**What operating system and version are you using?**

PS> Get-ComputerInfo -Property Windows*
WindowsBuildLabEx : 19041.1.amd64fre.vb_release.191206-1406
WindowsCurrentVersion : 6.3
WindowsEditionId : Core
WindowsInstallationType : Client
WindowsInstallDateFromRegistry : 03/05/2021 22:59:12
WindowsProductName : Windows 10 Home
WindowsRegisteredOrganization :
WindowsRegisteredOwner : ingo
WindowsSystemRoot : C:\WINDOWS
WindowsVersion : 2009
WindowsUBR : 1237

From a cmd prompt:

"C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Auxiliary\Build\vcvarsall.bat" amd64
**********************************************************************
** Visual Studio 2019 Developer Command Prompt v16.9.5
** Copyright (c) 2021 Microsoft Corporation
**********************************************************************
[vcvarsall.bat] Environment initialized for: 'x64'

**What compiler and version are you using?**

PS> cl
Microsoft (R) C/C++ Optimizing Compiler Version 19.28.29915 for x64
Copyright (C) Microsoft Corporation. All rights reserved.

cl : Command line error D8003 : missing source filename>

**What build system are you using?**

PS> cmake --version
cmake version 3.19.20122902-MSVC_2

CMake suite maintained and supported by Kitware (kitware.com/cmake).