BMessageFormat: parse the pattern at construction

* Instead of parsing the pattern everytime Format() is called, parse it
only once when the object is created.
* Adjust all callers to make use of the feature and reuse the instance
as much as possible. This also allows calling B_TRANSLATE only once
instead of everytime the formatting needs to be done. We use either a
static instance (when the message pattern is constant) or a field (when
it is not known to be constant).
* Since the BMessageFormat instances are now reused, add locking to
avoid race conditions (ICU itself is thread safe, but the format pattern
is recreated when the locale is changed)

src/apps/aboutsystem/AboutSystem.cpp

@@ -443,10 +443,12 @@ AboutView::AboutView()
 		B_ALIGN_VERTICAL_UNSET));
 
 	// CPU count, type and clock speed
-	BString processorLabel;
-	BMessageFormat().Format(processorLabel, B_TRANSLATE_COMMENT(
+	static BMessageFormat format(B_TRANSLATE_COMMENT(
 		"{0, plural, one{Processor:} other{# Processors:}}",
-		"\"Processor:\" or \"2 Processors:\""), systemInfo.cpu_count);
+		"\"Processor:\" or \"2 Processors:\""));
+
+	BString processorLabel;
+	format.Format(processorLabel, systemInfo.cpu_count);
 
 	uint32 topologyNodeCount = 0;
 	cpu_topology_node_info* topology = NULL;