[build] Make MODULE_GROUP mandatory for user modules

Make sure everything in the manifest has a group tag.

Change-Id: Id33e8ef34c148d6b18e34acc7a59466a3e18daf2

[zx] Magenta -> Zircon

The Great Renaming is here!

Change-Id: I3229bdeb2a3d0e40fb4db6fec8ca7d971fbffb94

[uapp][kilo] remove the kilo source from the build

This removes the only relative-path entry from the bootfs.manifest,
enabling mkbootfs to be run from anywhere.

Change-Id: I73384fbad539c7fa82b75df7c6b1413b0da54d71

[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

[build][musl] refer to musl libc as ulib/c

This makes the build rules and the intermediate
output files easier to understand, without having
to modify the path where musl libc lives.

The biggest observeable difference is the build
intermediate files:

$ ls build-magenta-pc-x86-64/ulib/c
config-module.h libc.abi.h libc.abi.stamp libc.so libc.so.id libc.so.strip
libc.a libc.abi.o libc.a.opts libc.so.abi libc.so.opts third_party

which previously were at build-magenta-pc-x86/ulib/musl
and named libmusl.*

and the replacing of ulib/musl with ulib/c in the library
dependencies of all the rules.mk files (the vast bulk of
this change)

Change-Id: If9c5d522099d2c9ac5bdb666b8e67a2eb3d316ee

[uapp][kilo] Fix Clang warnings

GCC and Clang both need a switch to disable warnings in this code.
But they support mutually exclusive switches.

Change-Id: I9298f58eb2164975762fa6a04592ca297ac7a829

[magenta] migrate from libddk to magenta/device headers

Change-Id: I91a8df001043635fa595d6fed1a6d6f092fc6b3e

[build] make musl-static the exception rather than musl-shared

This makes the common uapp, ulib, or utest rules.mk much more
comprehensible. Some day we'll eliminate the need for -static
entirely, but that requires some deeper refactoring.

Change-Id: Ifcdb635e5af7bf0b033632358164c3042e7e6d4a

[build] make dynamic linking the default

Now userapp/usertest modules are dynamic, and to build a static
binary userapp-static or usertest-static are used.

Change-Id: Ifd16f40a2bf23202ec17f3142f896abdec1c3271

[build] improve dynamic app linkage, make more apps dynamic

- userapp and usertest modules may not use MODULE_DEPS and
must use MODULE_LIBS or MODULE_STATIC_LIBS to declare
what libraries the depend on. Update all apps to comply
and generate a build error for apps that don't.
- no longer do fancy recursive resolution of static library
deps -- if you use MODULE_STATIC_LIBS it's up to you to
list all the ones you need.
- In practice this means a dynamic linked app including a
single static library will not accidentally pull in another
copy of libc or the like
- netsvc and others are now dynamic (and much smaller)

Change-Id: I2a9127e8dca90903b6a6e022c227a71c009c5659

[uapp][kilo] build Kilo editor for Magenta

It runs on the gfxconsole but is not entirely usable yet.
It's exposing some vt100 emulation and fileio bugs.

Change-Id: I4bd4ad32269bfe03b93aadc567700574cdc1649c