Fix handling of thumb symbols

The RE for matching apple- was typoed in ea29a0e6c. Additionally,
reverse the order of the two checks, since we use $3 and $4 to refer
to parts of one of the REs. Prior to ea29a0e6c the as_type check
was a plain string comparison, not a RE.
Move renaming of local symbols after checking for branch instructions

This simplifies identifying local symbols within the branch
heuristic block.
Add an option for trying to automatically add a prefix to external symbols
Move the initial handling of lines into parse_line

This allows doing the same cleanup on lines that don't come from
the initial cpp invocation read in the initial while (<ASMFILE>)
loop.
Add initial support for .include

This misses support for checking include directories specified
with -I parameters.
Don't comment out the whole line when handling .type

libopus piles up multiple directives on one line.
Only interpret .if if it's the first word of a line

The arm2gnu.pl script in libopus converts an IF (from a license
header) into a .if, which messed up gas-pp.
Comment out gnu specific stack notes on apple and armasm

Libav itself doesn't output these unless targeting ELF (where
they don't need to be commented out), but other projects (e.g.
OpenH264) have them unconditionally in the source.