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
The depot tool did not consistently distinct libraries from regular
targets when handling binary archives. The binary archive of a regular
target is located at <user>/<bin>/<arch>/<name> whereas a library is
located at <user>/<bin>/<arch>/<api>/<name>.
Fixes#2438
