doc: fix parallel build of html/man pages

The use of the same tempdir prevents building of these files in
parallel.
So build all of them in unique tempdirs so we can do them in parallel.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
ping6: allow disabling of openssl support

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
fix handling of CFLAGS

This defaults CFLAGS to -O3 without clobbering settings people have set
up in the environment already.

Also remove CC, because make provides a default CC so that code
will effectively never get used.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Tested-by: David Heidelberger <david.heidelberger@ixit.cz>
tftpd: check return value of set*id calls

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Reviewed-by: David Heidelberger <david.heidelberger@ixit.cz>