While integrating a newer libtool into GCC, an issue arose with what
value libtool was setting max_cmd_len to. This patch uses 'getconf
ARG_MAX' to set lt_cv_sys_max_cmd_len instead of going through a loop to
try and divine the right value, this should give a more accurate value
and should be faster too. getconf is a Posix command that most
platforms have and we drop into the old behaviour if it doesn't exist.
I originally thought about putting the getconf call before the case
statement (thus skipping the special case handling if getconf exists),
but then I thought it would be better to put the getconf usage into the
generic case only so that people could still have special case targets
if they wanted to avoid using getconf. If the special case targets want
to use getconf they can just delete their entry from the case statement
and fall into the generic case.