Disable signal handling in threads (see issue #1042)

I don't necessarily like having to do these extra calls whenever threads are
spawned (and what happens to signals during the time signal delivery is
disabled?) but it seems to fully fix os.execute.

NOTE: Also disables signals when loading openal, as it or one of its backends
spawns threads internally, and does not disable signals itself.

--HG--
branch : minor

src/modules/thread/threads.cpp

@@ -20,6 +20,10 @@
 
 #include "threads.h"
 
+#if defined(LOVE_LINUX)
+#include <signal.h>
+#endif
+
 namespace love
 {
 namespace thread
@@ -153,5 +157,21 @@ Conditional *ConditionalRef::operator->() const
 	return conditional;
 }
 
+#if defined(LOVE_LINUX)
+static sigset_t oldset;
+
+void disableSignals()
+{
+	sigset_t newset;
+	sigfillset(&newset);
+	pthread_sigmask(SIG_SETMASK, &newset, &oldset);
+}
+
+void reenableSignals()
+{
+	pthread_sigmask(SIG_SETMASK, &oldset, nullptr);
+}
+#endif
+
 } // thread
 } // love