autoconf: update pthread checks
Replace obsolete AC_TRY_COMPILE with AC_COMPILE_IFELSE. Replace shell
if/then conditionals with AS_IF macros. Reformat indentation and
quoting.
This change was done manually, since autoupdate copes poorly with the
old, nested AC_TRY_COMPILE macros.
Change-Id: I2c34d1426f154daff65999076821f49ddaa16a24
Reviewed-on: https://gerrit.openafs.org/13018
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Marcio Brito Barbosa <mbarbosa@sinenomine.net>