src/thread/meson.build: detect pthread_setname_np()

This compile-time check got lost during the Meson transition.

src/thread/meson.build

@@ -1,10 +1,14 @@
+threads_dep = dependency('threads')
+
+conf.set('HAVE_PTHREAD_SETNAME_NP', compiler.has_function('pthread_setname_np', dependencies: threads_dep))
+
 thread = static_library(
   'thread',
   'Util.cxx',
   'Thread.cxx',
   include_directories: inc,
   dependencies: [
-    dependency('threads')
+    threads_dep,
   ],
 )