Clean up error returns for unsupported pthread mutex/cond attr values

NaCl does not support process-shared pthread mutexes or cond variables.
glibc's libpthread functions should report proper errors for that.
Likewise NaCl does not support pthread_condattr_setclock for any clock
value other than CLOCK_REALTIME, but the proper error code for
CLOCK_MONOTONIC is ENOTSUP rather than EINVAL (because CLOCK_MONOTONIC
is a "known clock" for other purposes, just not supported for this one).

Returning ENOTSUP for these cases is consistent with what the new
(upstream) glibc does.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=4142
TEST= toolchain trybots
R=phosek@chromium.org, sbc@chromium.org

Review URL: https://codereview.chromium.org/1234673002 .
3 files changed