process: replace crucible::gettid() with a weak symbol

Since we're now using weak symbols for dodgy libc functions, we might
as well do it for gettid() too.

Use the ::gettid() global namespace and let libc override it.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>

include/crucible/lockset.h

@@ -117,7 +117,7 @@ namespace crucible {
 		while (full() || locked(name)) {
 			m_condvar.wait(lock);
 		}
-		auto rv = m_set.insert(make_pair(name, crucible::gettid()));
+		auto rv = m_set.insert(make_pair(name, gettid()));
 		THROW_CHECK0(runtime_error, rv.second);
 	}
 
@@ -129,7 +129,7 @@ namespace crucible {
 		if (full() || locked(name)) {
 			return false;
 		}
-		auto rv = m_set.insert(make_pair(name, crucible::gettid()));
+		auto rv = m_set.insert(make_pair(name, gettid()));
 		THROW_CHECK1(runtime_error, name, rv.second);
 		return true;
 	}

include/crucible/process.h

@@ -10,6 +10,10 @@
 #include <sys/wait.h>
 #include <unistd.h>
 
+extern "C" {
+	pid_t gettid() throw();
+};
+
 namespace crucible {
 	using namespace std;
 
@@ -73,7 +77,6 @@ namespace crucible {
 
 	typedef ResourceHandle<Process::id, Process> Pid;
 
-	pid_t gettid();
 	double getloadavg1();
 	double getloadavg5();
 	double getloadavg15();