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

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

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.

gcc/testsuite/

2019-07-26  Iain Sandoe  <iain@sandoe.co.uk>

	* lib/scanasm.exp (object-size): Handle Darwin's size command.

From-SVN: r273839