Itanium HP-UX build failure, register stack

The code we added recently to the stack-depth check to also check the
register stack on ia64 doesn't compile on HP-UX B.11.31, using the HP
aCC compiler:

cc -Ae +O2 -g -I../../../src/include -D_XOPEN_SOURCE_EXTENDED -c -o
postgres.o postgres.c
"postgres.c", line 3002: warning #2837-D: omission of explicit type is
nonstandard ("int" assumed)
static __inline__ char *
^

"postgres.c", line 3002: error #2065: expected a ";"
static __inline__ char *
^

I committed a fix for that using the HP-UX specific _Asm_mov_from_ar
macro, similar to how we use _Asm_xchg for TAS().

With this, 8.4 compiles on HP-UX again, yeaee! 9.0 still has this issue:
http://archives.postgresql.org/pgsql-hackers/2010-11/msg01971.php. I'll
take a look at that..

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com