Changed default optimize level from -O (which is actually O1) to -Og
which is basically O1, but flags are tailored to make debugging it
easier than O1 and even O0.
Archive libraries are now deleted before they are created. For some
reason AR and RANLIB will attempt to reuse the old file, which will
result in a "this file is corrupted" message, so they need to be
deleted first to indicate to them that they need to create the file.
BUILD TOOLS variable PLUGIN has been added to find the path to the LTO
plugin. This will put to use in a later commit when LTO is enabled.
Will be removed if it is decided to not enable LTO due to issues with
debugging.