Bypass the -pthread -shared check for unknown platforms

[Jisi Liu, 2010-12-08 17:45:32]

Hmm, so I was testing protobuf on Mac OS..
It turns out the -phthread and -shared consistency part doesn't work for Mac OS.

Before a previous acx_pthread.m4 fix, the first part of logic was inverted
(against the comments). So actually most of platforms did bypass the check.

After the fix, it works well on x86 linux, but failed on Mac OS.
Mac OS actually accept the -z LD flag (opposed to the comments), but there's no
case in the tests cover Mac OS. I searched to see if there's some update of the
script, but unfortunately the original site seems to be moved to git based, and
I didn't find the up-to-date script..

So for now, I guess we should just let it be when the script failed to find a
testcase for -pthread and -shared.  Set the acx_pthread_ok to false will fail
the whole protobuf compiling.

[kenton, 2010-12-09 01:10:21]

http://codereview.appspot.com/3434045/diff/1/m4/acx_pthread.m4
File m4/acx_pthread.m4 (right):

http://codereview.appspot.com/3434045/diff/1/m4/acx_pthread.m4#newcode284
m4/acx_pthread.m4:284: AC_MSG_CHECKING([whether -pthread is sufficient with
-shared])
I think what we want to do is figure out why this check fails on OSX, and fix
it.  Can you find it in config.log?