Link programs with pthread via cmake

All programs are now linked directly with all test code, thus adding a
pthread abstraction into the test code means having to link the programs
with pthread (if the library is found under cmake).

Signed-off-by: Paul Elliott <paul.elliott@arm.com>
diff --git a/programs/ssl/CMakeLists.txt b/programs/ssl/CMakeLists.txt
index 280bbcf..8ffa854 100644
--- a/programs/ssl/CMakeLists.txt
+++ b/programs/ssl/CMakeLists.txt
@@ -39,7 +39,7 @@
     endif()
     add_executable(${exe} ${exe}.c $<TARGET_OBJECTS:mbedtls_test>
         ${extra_sources})
-    target_link_libraries(${exe} ${libs})
+    target_link_libraries(${exe} ${libs} ${CMAKE_THREAD_LIBS_INIT})
     target_include_directories(${exe} PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/../../tests/include)
     if(exe STREQUAL "ssl_client2" OR exe STREQUAL "ssl_server2")
         if(GEN_FILES)