[cmake] static build: populate private

in pkg-config files only add Requires.private and Libs.private if we
build a static library.

server/CMakeLists.txt

@@ -77,6 +77,12 @@ foreach(FREERDP_SERVER ${FREERDP_EXTRA_SERVERS})
   add_subdirectory(${FREERDP_SERVER})
 endforeach()
 
+# Do not set Requires.Private if not a static build
+if(NOT BUILD_SHARED_LIBS)
+  set(FREERDP_SERVER_PC_REQUIRES_PRIVATE "freerdp${FREERDP_API_VERSION}")
+  set(FREERDP_SERVER_PC_LIBRARY_PRIVATE "-ldl -lpthread")
+endif()
+
 include(pkg-config-install-prefix)
 cleaning_configure_file(
   ${CMAKE_CURRENT_SOURCE_DIR}/freerdp-server.pc.in