liblangutil: SourceLocation to default initialize data members (w/o the use of ctor)

See: http://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#c45-dont-define-a-default-constructor-that-only-initializes-data-members-use-in-class-member-initializers-instead

test/libevmasm/Optimiser.cpp

@@ -53,7 +53,7 @@ namespace
 		// add dummy locations to each item so that we can check that they are not deleted
 		AssemblyItems input = _input;
 		for (AssemblyItem& item: input)
-			item.setLocation(SourceLocation(1, 3, nullptr));
+			item.setLocation({1, 3, nullptr});
 		return input;
 	}