This is yet another collection of fixes from the build-infra hotspot project forest that has a stand-alone value.

The most important change is the support of a new log option, cmdlines. This is, like the old "nofile", an option that can be added to a log level, e.g. "LOG=info,cmdlines" or used standalone "LOG=cmdlines" (in which case the log level stays at default). With this in place, the command line of "important" commands are printed. Examples of "important" commands are compiler and linker calls. Examples of "non-important" commands are "mkdir" or "cat". Note that at this point, not all "important" calls are identified, typically in esoteric stuff like gensrc.

Apart from this, a few other changes are also included:
* Allow DEBUG_SYMBOLS to be individually turned off (follow up to JDK-8145596)
* Support .S assembly files
* Expose USERNAME outside configure
* Fix broken indentation