opr: Disable some warnings during opr assertions
Detect _Pragma(), a C99 extension for inline #pragma's, and use it to
disable to certain warnings during the use of opr_Verify() and
opr_Assert().
Because some versions of clang support _Pragma, do not have support
for -Wtautological-pointer-compare, and do set -Werror and -Wunknown-pragmas,
we must explicitly check for pragma support for -Wtautological-pointer-compare
as well.
Change-Id: Id3d5ee347f320a366a0571572b58414aa7044bf7
Reviewed-on: http://gerrit.openafs.org/11852
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>