The dependency tracking still doesn't need any specific ordering to
build, but it's better to build DevTools and Libraries first so it
doesn't try to build two Applications that each need to wait for
libraries to be built, wasting a make child sitting around trying to
acquire the lock on the library directory.
Lock each directory before entering it so when using -j, the same
dependency isn't built more than once at a time.
This doesn't get full -j parallelism though, since one make child
will be sitting idle waiting for flock to receive its lock and
continue making (which should then do nothing since it will have
been built already). Unfortunately there's not much that can be
done to fix that since it can't proceed until its dependency is
built by another make process.
Tests fail to compile for a mix of reasons, some due to macOS file systems being by default case-insensitive and some specific to clang. Both issues are better left to a dedicated set of PR that addressed them.
Instead of directly manipulating LDFLAGS, set LIB_DEPS in each
subdirectory Makefile listing the libraries needed for
building/linking such as "LIB_DEPS = Core GUI Draw IPC Core".
This adds each library as an -L and -l argument in LDFLAGS, but
also adds the library.a file as a link dependency on the current
$(PROGRAM). This causes the given library to be (re)built before
linking the current $(PROGRAM), but will also re-link any binaries
depending on that library when it is modified, when running make
from the root directory.
Also turn generator tools like IPCCompiler into dependencies on the
files they generate, so they are built on-demand when a particular
directory needs them.
This all allows the root Makefile to just list directories and not
care about the order, as all of the dependency tracking will figure
it out.
Allow everything to be built from the top level directory with just
'make', cleaned with 'make clean', and installed with 'make
install'. Also support these in any particular subdirectory.
Specifying 'make VERBOSE=1' will print each ld/g++/etc. command as
it runs.
Kernel and early host tools (IPCCompiler, etc.) are built as
object.host.o so that they don't conflict with other things built
with the cross-compiler.
