Before, ccache's configure stage built HTML documentation and man pages
depending on if asciidoc is installed. This patch makes it configurable.
Pass the new cmake option BUILD_DOCS along and add the asciidoc
dependency if necessary.
This fixes an issue when ccache's configure stage found asciidoc/a2x on
the system outside of the sysroot (e.g. installed via 'apt install
asciidoc'). ccache would then decide to build docs and manual pages, but
would fail during compilation: the system's a2x could not find the
system's asciidoc because it did not reside in the set PATH.
By enabling/disabling docs/man page generation explicitly and adding
asciidoc to DEPENDS as necessary, this is no longer an issue.
Signed-off-by: Bastian Krause <bst@pengutronix.de> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
