openssl: fix gentoo specific stuff (use of "has" command)

this copy/paste error somehow survived for quite a long time in the build
without being noticed - there is no "has" command in sabotage.
since due to the error previously the else branch of that code was taken,
and it's known working, we just use that path now directly.
openssl: use -isystem rather than -I for crosscompile

the reason for using -I explicitly there was that openssl build system
somehow parses the CFLAGS for what looks like directories names, makes
some invalid assumptions and then breaks the build like:
target already defined - linux-generic32
(offending arg: $sysroot/include)
however i found that -isystem can be concatenated directly with the pathname
just like with -I, so we can workaround this issue.
the advantage of using -isystem is that musl headers there are treated as
system headers, so warnings are disabled for them.
with -I, the build log was full of warning spawm about __bswap inline functions
in endian.h.