[Patch gas/mach-o 0/2] implement mach-o subsections-via-symbols.

[Iain Sandoe]

Hello All,

The Darwin/Mach-O object file and native linker support a form of sub- 
sectioning that is driven solely by externally visible symbols.

thus code like:

_label1:
	some instructions
_label2:
	some more instructions
Localabel:
	even more instructions
----

can be split up by the linker into two 'atoms' one starting with  
_label1, and one with _label2.

local symbols (beginning 'L', for mach-o) are not considered in this -  
thus the code starting with "Localsym" in the example would remain  
attached to the subsection starting with _label2.

The code in the two following patches is Tristan's implementation of  
this rebased against trunk - with (extremely) minor adjustments by me.

Patch 1 is the changes that touch files other than mach-o ones - and  
needs review as appropriate.

Patch 2 is the changes to config/mach-o.{c,h} which include my minor  
adjustments.

cheers
Iain