TAS patch for building on armel/armhf thumb

Hello,

if you build postgresql (tested all releases from 8.4 up to trunk) for
ARM with the -mthumb instruction set (much better performance), it
fails with

gcc -g -O2 -g -Wall -O2 -fPIC -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Wendif-labels
-fno-strict-aliasing-fwrapv -g -I../../../../src/include -D_GNU_SOURCE -I/usr/include/libxml2 -I/usr/include/tcl8.5 -c
-oxlog.o xlog.c 
/tmp/cc8Wkglp.s: Assembler messages:
/tmp/cc8Wkglp.s:1456: Error: selected processor does not support `swpb r3,r3,[r0]'
/tmp/cc8Wkglp.s:1587: Error: selected processor does not support `swpb r2,r2,[r0]'

A fair while ago, Alexander Sack from Linaro applied a patch to our
packages to drop the Assembler bits and instead use gcc's atomic
builtins [1], which provide a proper implementation for thumb, too.

The original patch spectacularly failed on our slightly newer Panda
boards (our old builders were Freescale Babbage boards), but I got
that to work yesterday. Now it's working on Babbage, Panda, both with
and without hard float (armhf) enabled.

I'm not sure how appropriate it is for upstream to have GCC-isms in
the code, but even if it can't land upstream, perhaps it is useful for
other porters/packagers.

Thanks,

Martin

[1] http://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/Atomic-Builtins.html
--
Martin Pitt                        | http://www.piware.de
Ubuntu Developer (www.ubuntu.com)  | Debian Developer  (www.debian.org)