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/audio/openal/Audio.cpp

@@ -96,6 +96,11 @@ Audio::Audio()
 	, poolThread(nullptr)
 	, distanceModel(DISTANCE_INVERSE_CLAMPED)
 {
+#if defined(LOVE_LINUX)
+	// Temporarly block signals, as the thread inherits this mask
+	love::thread::disableSignals();
+#endif
+
 	// Passing null for default device.
 	device = alcOpenDevice(nullptr);
 
@@ -116,6 +121,10 @@ Audio::Audio()
 	if (!alcMakeContextCurrent(context) || alcGetError(device) != ALC_NO_ERROR)
 		throw love::Exception("Could not make context current.");
 
+#if defined(LOVE_LINUX)
+	love::thread::reenableSignals();
+#endif
+
 #ifdef ALC_EXT_EFX
 	initializeEFX();