wsd: always use signal-safe calls

The async-signal-safe functions to get thread-id
and thread-name, which cache the results, are
faster, cleaner, and signal-safe. No reason why
we shouldn't always use them.

Especially since it appears the logic was
inverted in Log::prefix, such that the signal
un-safe calls were made during signal-handling,
and the safe ones were called otherwise!

Instead of passing the signal-safe flag to
Log::prefix, we pass the buffer size, for
improved security.

Furthermore, reduce header dependencies
and reduce clutter.

Change-Id: I697689b2f0a290b6d8cce4babc3ac1e576141da6

common/Seccomp.cpp

@@ -12,6 +12,9 @@
  */
 
 #include <config.h>
+
+#include "Seccomp.hpp"
+
 #include <dlfcn.h>
 #include <ftw.h>
 #include <linux/audit.h>
@@ -31,7 +34,6 @@
 
 #include <common/Log.hpp>
 #include <common/SigUtil.hpp>
-#include "Seccomp.hpp"
 
 #if DISABLE_SECCOMP == 0
 #ifndef SYS_SECCOMP