Add a Python script to take an executable, run gdb to disassemble a function,

read the memory contents of the function, and then feed the bytes to the
'llvm-mc -disassemble' command.

It uses the pexpect module located under ToT/test/pexpect-2.4 directory to
automate the interaction with gdb.  This is used initially to test the low
level ARM disassembler of llvm.

llvm-svn: 127785