base-nova: fully qualify Utcb type
build system: Back out on error at libdep stage
Tool for preparing a single 3rd-party port

Issue #1082
Build-system support for ported 3rd-party code

The new 'select_from_ports' function allows a target description file to
query the path to an installed port. All ports are stored in a central
location specified as CONTRIB_DIR. By default, CONTRIB_DIR is defined
as '<genode-dir>/contrib'. Ports of 3rd-party source code are managed
using the tools at '<genode-dir>/tool/ports/'.

Issue #1082
tool/prepare.mk: Switch directories silently
Build-system support for creating host tools
libports: migrate to new ports mechanism

Issue #1082
base-okl4: migrate to new ports mechanism

Issue #1082
base-nova: migrate to new ports mechanism

Issue #1082
dde_oss: migrate to new ports mechanism

Issue #1082
ports: migrate to new ports mechanism

Issue #1082
ports-foc: migrate to new ports mechanism

Issue #1082
dde_linux: migrate to new ports mechanism

Issue #1082
dde_ipxe: migrate to new ports mechanism

Issue #1082
base-foc: migrate to new ports mechanism

Issue #1082
base-fiasco: migrate to new ports mechanism

Issue #1082
base-pistachio: migrate to new ports mechanism

Issue #1082
Temporarily disable hash checks

...until the transition to the new ports management is complete.
doc: Description of HOST_TOOLS mechanism
doc: Uniform markup of the build-system manual

Use _italic_ for path names rather than 'verbatim'. Because path names
tend to be quite long, the overly use of verbatim makes paragraphs hard
to read.