The depot tool 'build_bin_archive' used to ask only whether CCACHE is empty or
not and, if it wasn't empty, the tool added 'CCACHE := yes' to the build.conf
of the temporary build dir. This caused the sub-build processes to use ccache
even when the top-level CCACHE variable was set to a bogus value.
Also adds documentation of the CCACHE variable to the help message of the
'build' and 'build_bin_archive' tool.
Ref #4212
This commit complements issue #4004 with support for the depot/create
tool. If CCACHE=1 is specified at the command line, the build directory
for building a binary archive is configured with 'CCACHE := yes'.
This patch changes the depot layout such that each archive is
represented as a directory that contains the versions of the archive as
subdirectories.
Issue #2610
When building with multiple jobs, the 'Makefile' rule may be executed
before any of its sibling rules, which implicitly create the target
directory. In this case, the attempt to create the symlink for
'Makefile' fails and the 'build_bin_archive' aborts. Analogously to the
sibling rules, this fix creates the target directory as a side effect of
the 'Makefile' rule.
