Special epilogue for vararg functions. We cannot do a pop to pc because

Special epilogue for vararg functions. We cannot do a pop to pc because
there follows a sp increment for the va register save region. Instead issue
a separate pop to another register, increment sp, and then return:
        pop {r4, r5, r6, r7}
        pop {r3}
        add sp, #3 * 4
        bx r3

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@33739 91177308-0d34-0410-b5e6-96231b3b80d8