Fix finding winpthreads (#2171)

Author: isuruf

CMake/FindPThreads.cmake

@@ -9,7 +9,7 @@ if (PThreads_INCLUDE_DIRS AND PThreads_LIBRARIES)
 endif (PThreads_INCLUDE_DIRS AND PThreads_LIBRARIES)
 
 find_path(PThreads_INCLUDE_DIRS NAMES pthread.h )
-find_library(PThreads_LIBRARIES NAMES pthreads libpthreads )
+find_library(PThreads_LIBRARIES NAMES pthread pthreads libpthreads )
 
 include(FindPackageHandleStandardArgs)
 FIND_PACKAGE_HANDLE_STANDARD_ARGS(PThreads DEFAULT_MSG PThreads_INCLUDE_DIRS PThreads_LIBRARIES)

CMakeLists.txt

@@ -133,14 +133,7 @@ if(MSVC)
         set(PThreads_LIBRARIES PThreads4W::PThreads4W)
         set(PThreads_INCLUDE_DIRS ${PThreads4W_INCLUDE_DIRS})
     else()
-        find_package(PThreads)
-        if(NOT PThreads_FOUND)
-            include(CheckIncludeFile)
-            check_include_file(pthread.h HAVE_PTHREAD_H)
-            if(NOT HAVE_PTHREAD_H)
-                message(FATAL_ERROR "Could not find pthreads.")
-            endif()
-        endif()
+        find_package(PThreads REQUIRED)
     endif()
     set(FLINT_USES_PTHREAD ON CACHE BOOL "Use POSIX Threads.")
 else()