Fix modified immediate bug reported by MC Hammer.

Instructions of the form [ADD Rd, pc, #imm] are manually aliased
in processInstruction() to use ADR. To accomodate this, mod_imm handling
had to be tweaked a bit. Turns out it was the manual aliasing that must
be tweaked to accommodate mod_imms instead. More information about the
parsed instruction is available at the point where processInstruction()
is invoked, which makes it easier to detect a mod_imm at that point rather
than trying to detect a potential alias when a mod_imm is being prepped.
Added a test case and fixed some white spaces as well.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223772 91177308-0d34-0410-b5e6-96231b3b80d8
Removing an unused variable to silence a -Wunused-but-set-variable warning. NFC.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223773 91177308-0d34-0410-b5e6-96231b3b80d8