pgsql: Clean up icc + ia64 situation.

Clean up icc + ia64 situation.

Some googling turned up multiple sources saying that older versions of icc
do not accept gcc-compatible asm blocks on IA64, though asm does work on
x86[_64].  This is apparently fixed as of icc version 12.0 or so, but that
doesn't help us much; if we have to carry the extra implementation anyway,
we may as well just use it for icc rather than add a compiler version test.

Hence, revert commit 2c713d6ea29c91cd2cbd92fa801a61e55ea2a3c4 (though I
separated the icc code from the gcc code completely, producing what seems
cleaner code).  Document the state of affairs more explicitly, both in
s_lock.h and postgres.c, and make some cosmetic adjustments around the
IA64 code in s_lock.h.

Branch
------
master

Details
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http://git.postgresql.org/pg/commitdiff/123c9d2fc1fe0a8ee676d8244198b34a5e99ea90

Modified Files
--------------
src/backend/tcop/postgres.c  |   10 +++++++++-
src/include/storage/s_lock.h |   29 +++++++++++++++++------------
2 files changed, 26 insertions(+), 13 deletions(-)