ARM: preserve undef flag in pseudo instruction expanders

Copy over the whole register machine operand instead of creating a new one
with an incomplete set of flags.
ARM: do not add a regmask for TAILJUMPs

The jump doesn't really kill the registers, the following call does but
we never get back anyway.
This avoids some verify-machineinstrs problems when TAILJUMPs are
if-converted.
ARM: optimizeSelect has to consider the previous register class

optimizeSelect folds (predicated) copy instructions, it must not ignore
the original register class of the operand when replacing the register
with the copies dest register.
Fix typo
Fix indentation