[Darwin, testsuite] Handle Darwin's size command.

[Mike Stump]

On Jul 26, 2019, at 7:52 AM, Iain Sandoe <iain@sandoe.co.uk> wrote:
> 
> This one has been in my patch stack for a long time…
> 
> Darwin's "size" command has a different header line, reflecting the Mach-O
> section naming conventions.  This causes tests using the command to fail
> because scanasm.exp expects and checks specific layout of the header line.
> 
> Tested on i686, x86_64 and powerpc darwin and x86_64,powerpc-linux-gnu
> 
> OK for trunk?

Ok.