[RFC] code changes/removal in boot2.c and ufsread.c so clang can compile boot2

[Alexander Best]

hi everybody,

r218745 triggered quite a discussion about dead code in boot2.c. i talked to
roman (rdivacky@) and we were trying to improve the situation so that boot2
would build with clang 2.8 (base) and the latest development version of
clang (trunk). a lot of the ideas came from Bruce (bde@).

i'd really appreciate, if somebody could have a look at this patchset. for me
it strips down the boot2 code so clang is able to compile it just fine. please
bear in mind that this has to work with boot2 supporting UFS1 *and* UFS2. so
please be sure not to override BOOT2_UFS in your src.conf or some place else.

you should be able to test the (hopefully sucessfully) compiled boot2 binary
by copying it to /boot. please be sure to keep a backup of your existing boot2
file in case something breaks.

the patchset (against a recent HEAD) can be found here:
http://people.freebsd.org/~arundel/patches/boot2.c.diff2

cheers.
alex

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a13x