Simplify pthreads library detection

Use the cmake builtin Threads library detection, and bail out if it
wasn't pthreads. This allows deleting the cmake/FindPTHREAD.cmake file
which complains because pthreads doesn't provide a pkg-config file.

In newer versions of cmake the FindThreads module has the
THREADS_PREFER_PTHREAD_FLAG variable and creates a Threads::Threads
import target. However, in order top remain compatible with older
cmake version this is not used.

CMakeLists.txt

@@ -191,7 +191,13 @@ add_custom_target(uninstall
         "${CMAKE_COMMAND}" -P "${CMAKE_CURRENT_BINARY_DIR}/cmake_uninstall.cmake")
 
 find_required_package(GTK)
-find_required_package(PTHREAD)
+
+set(CMAKE_THREAD_PREFER_PTHREAD TRUE)
+find_package(Threads REQUIRED)
+if(NOT CMAKE_USE_PTHREADS_INIT)
+        message(FATAL_ERROR "pthreads thread library not found")
+endif()
+
 find_suggested_package(GCRYPT)
 find_suggested_package(AVAHI)
 

remmina-plugins/CMakeLists.txt

@@ -44,7 +44,7 @@ set(APPICON16_EMBLEMS_DIR "${REMMINA_DATADIR}/icons/hicolor/16x16/emblems")
 set(APPICON22_EMBLEMS_DIR "${REMMINA_DATADIR}/icons/hicolor/22x22/emblems")
 
 set(REMMINA_COMMON_INCLUDE_DIRS ${GTK_INCLUDE_DIRS})
-set(REMMINA_COMMON_LIBRARIES ${GTK_LIBRARIES} ${PTHREAD_LIBRARY})
+set(REMMINA_COMMON_LIBRARIES ${GTK_LIBRARIES} ${CMAKE_THREAD_LIBS_INIT})
 
 find_suggested_package(LIBSSH)
 if(LIBSSH_FOUND)

remmina-plugins/rdp/CMakeLists.txt

@@ -32,8 +32,8 @@
 # files in the program, then also delete it here.
 
 
-set(CMAKE_THREAD_PREFER_PTHREAD)
-find_package(Threads)
+set(CMAKE_THREAD_PREFER_PTHREAD TRUE)
+find_package(Threads REQUIRED)
 find_package(X11)
 
 set(REMMINA_PLUGIN_RDP_SRCS

remmina/CMakeLists.txt

@@ -123,18 +123,15 @@ find_package(X11)
 include_directories(${X11_INCLUDE_DIR})
 target_link_libraries(remmina ${X11_LIBRARIES})
 
+target_link_libraries(remmina ${CMAKE_THREAD_LIBS_INIT})
+
 find_suggested_package(LIBSSH)
 if(LIBSSH_FOUND)
         add_definitions(-DHAVE_LIBSSH)
         include_directories(${LIBSSH_INCLUDE_DIRS})
         target_link_libraries(remmina ${LIBSSH_LIBRARIES})
 endif()
 
-if(PTHREAD_FOUND)
-        include_directories(${PTHREAD_INCLUDE_DIRS})
-        target_link_libraries(remmina ${PTHREAD_LIBRARIES})
-endif()
-
 if(GCRYPT_FOUND)
         include_directories(${GCRYPT_INCLUDE_DIRS})
         target_link_libraries(remmina ${GCRYPT_LIBRARIES})