build: there have been missing build files

there are the 3 files in ecore. However, they have not been tested,
there are additionally no examples at all, which did not bring up the
missing API calls, now they are here.

Note: they are compiling, however, it seems that it is not working right
now.

src/lib/ecore/meson.build

@@ -175,7 +175,10 @@ ecore_src = [
   'ecore_exe_private.h',
   'ecore_private.h',
   'ecore_internal.h',
-  'ecore_main_common.h'
+  'ecore_main_common.h',
+  'efl_exe.c',
+  'efl_thread.c',
+  'efl_threadio.c',
 ]
 
 if sys_windows == true