INSTALL, cmd.mk, install-man.mk: Support installing compressed pages

Distributions usually install compressed (.gz) pages to reduce space.
Let's support this in our build system, as a command-line variable "Z",
which is empty by default, but can be set to a file extension to append
to the page names (and the appropriate compression program will be
used).  For now, the only compression supported is ".gz".

Example:

    $ make install Z=.gz

This can be combined with LINK_PAGES, to produce compressed pages and
use symbolic links for the link pages:

    $ make install Z=.gz LINK_PAGES=symlink

Signed-off-by: Alejandro Colomar <alx@kernel.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/INSTALL b/INSTALL
index 63bbf169b..d542bd7c5 100644
--- a/INSTALL
+++ b/INSTALL
@@ -84,8 +84,11 @@ Description
              -  xargs(1)
 
           -  For installing:
+             -  gzip(1)
              -  install(1)
              -  ln(1)
+             -  sponge(1)
+             -  test(1)
 
           -  For uninstalling / cleaning:
              -  rm(1)