pre_flush_set and post_flush_set are almost always empty, so we can use
extend() instead of a for...in loop to add the previous elements of
self._container.
We can also skip the conversion from deque to list since pre_flush is
always appended on the right side.
On a QEMU build the time spent in flush_pre_post goes from 1.4 to 0.5
seconds.
Since the CompileArgs class already needs to know about the compiler,
and we really need at least per-lanaguage if not per-compiler
CompilerArgs classes, let's get the CompilerArgs instance from the
compiler using a method.
Christian Clauss