[run-zircon] Add --debugger to run-zircon

- Adds DEBUG_HARD to make-parallel. If true, the build
will be built with -O0 -g3
- Move GLOBAL_OPTFLAGS and MODULE_OPTFLAGS later in the gcc flag list
so that they can override GLOBAL/KERNEL/ARCH flags as necessary.
- --debugger will start qemu with a GDB stub waiting for
connection.

Change-Id: I7f2425ef1f4f55c83ecd2f0e50197777af466c23

[make] add QUIET=1 option to the build to squelch all output

Change-Id: I57742bb6aa0ad1f0dc516c917dfecd65f6f65f43

[build] flatten the build

Previously we treated kernel/, system/, and third_party/ as
overlays on a shared namespace. This required the concept
of "canonical" module names, and a lot of complexity to ensure
that things didn't collide and the build worked.

This change gets rid of that, no longer passes -I to make,
so that include directives from our *.mk files do not magically
wildcard across various paths, etc.

The most user-visible change is that everywhere where a module
name is specified (MODULE_DEPS, MODULE_LIBS, etc), full module
names like kernel/lib/io or system/ulib/mxio must be used instead
of previously-allowed "short" names like lib/io and ulib/mxio.

The build output still has a similar shape, but the first segment
of the module path (kernel/, system/, or third_party/) is no
longer elided under $(BUILDDIR)

Change-Id: I525aba1da1c86eb7a86007bddc669f7eeebfedd5