Gdbarch documentation in the internals manual

[Stan Shebs]

While poking through the gdbarch description bits in the internals 
manual, I noticed a general disconnect between what the manual describes 
and what developers actually use. Namely, the manual usually describes 
the getters, while people actually use the setters to fill in gdbarch 
objects; and I didn't see anywhere where the manual says "each 
gdbarch_foo also has a set_gdbarch_foo that you can use when filling in 
a gdbarch". (Yes one could surmise that from studying the sources, but 
the point of the manual is to reduce the need to read all the code.) 
Sometimes, as with frame_align, the "gdbarch_" part is left off also.

At the very least the manual needs to mention the pairing of gdbarch_foo 
/ set_gdbarch_foo pairs, and probably gdbarch_foo_p also. What I'm 
wondering is, should we describe the functions in their getter form, or 
switch to describing the setters, or always list both? I'm working on a 
little script that will complain about discrepancies between source and 
manual, so once we decide, we will have a way to catch future 
inconsistencies.

Stan