Prevent a possible deadlock in the linker script when using goma.

Prevent a possible deadlock in the linker script when using goma.

Make (and now ninja) run ld under flock. Goma allows only a limited
number N of local gcc processes, which it does by running a custom gcc.

If N gcc processes are trying to run a link, N-1 will be waiting on
flock. The Nth process then tries to call an N+1th gcc process to determine the
bitness of the system, which blocks.

As a workaround, use getconf to determine bitness instead.
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=122292

[Lei Zhang, 2012-02-16 03:23:45]

I don't have a 64-bit kernel / 32-bit userland configuration, so I'm not sure if
getconf will return the bit-ness of the kernel or of the userland.

If you have already tested this, then LG. Otherwise, I'd ask cmp if we have a
machine on the waterfall (e.g. the 32-bit Linux clobber bot) that has this mixed
configuration, and check what getconf returns there.

[Nico, 2012-02-16 03:26:21]

On 2012/02/16 03:23:45, Lei Zhang wrote:
> I don't have a 64-bit kernel / 32-bit userland configuration, so I'm not sure
if
> getconf will return the bit-ness of the kernel or of the userland.
> 
> If you have already tested this, then LG. Otherwise, I'd ask cmp if we have a
> machine on the waterfall (e.g. the 32-bit Linux clobber bot) that has this
mixed
> configuration, and check what getconf returns there.

Forgot to say: I sshd into the 32bit linux clobber builder on the main waterfall
and verified that `getconf LONG_BIT` returns 32 over there. (uname -a says
i686.) So this should be fine.

[Lei Zhang, 2012-02-16 03:40:00]

On 2012/02/16 03:26:21, Nico wrote:
> On 2012/02/16 03:23:45, Lei Zhang wrote:
> > I don't have a 64-bit kernel / 32-bit userland configuration, so I'm not
sure
> if
> > getconf will return the bit-ness of the kernel or of the userland.
> > 
> > If you have already tested this, then LG. Otherwise, I'd ask cmp if we have
a
> > machine on the waterfall (e.g. the 32-bit Linux clobber bot) that has this
> mixed
> > configuration, and check what getconf returns there.
> 
> Forgot to say: I sshd into the 32bit linux clobber builder on the main
waterfall
> and verified that `getconf LONG_BIT` returns 32 over there. (uname -a says
> i686.) So this should be fine.

Hmm, no. That bot has a 32-bit kernel with PAE turned on. The mixed environment
I speak of is when uname -m says x86_64, but the userland is 32-bit. In any
case, I looked at the getconf code and it calls sysconf(_SC_LONG_BIT), which is
userland, so LGTM.

[Evan Martin, 2012-02-16 16:12:19]

LGTM if you're willing to deal with bot fallout ;)