pgsql: Use a non-locking test in TAS_SPIN() on all IA64 platforms.

Use a non-locking test in TAS_SPIN() on all IA64 platforms.

Per my testing, this works just as well with gcc as it does with HP's
compiler; and there is no reason to think that the effect doesn't occur
with icc, either.

Also, rewrite the header comment about enforcing sequencing around spinlock
operations, per Robert's gripe that it was misleading.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/be1e8053f48f76ac718a03d6526e34e2f2489f5c

Modified Files
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src/include/storage/s_lock.h | 28 ++++++++++++++++++++++------
1 files changed, 22 insertions(+), 6 deletions(-)