Add cfi instr for CFA calculation when movpc is expanded to call and pop

Add cfi instr for CFA calculation when movpc is expanded to call and pop

This fixes the issue of wrong CFA calculation in the following case:

0x08048400 <+0>:	push   %ebx
0x08048401 <+1>:	sub    $0x8,%esp
0x08048404 <+4>:	**call   0x8048409 <test+9>**
0x08048409 <+9>:	**pop    %eax**
0x0804840a <+10>:	add    $0x1bf7,%eax
0x08048410 <+16>:	mov    %eax,%ebx
0x08048412 <+18>:	call   0x80483f0 <bar>
0x08048417 <+23>:	add    $0x8,%esp
0x0804841a <+26>:	pop    %ebx
0x0804841b <+27>:	ret

The highlighted instructions are a product of movpc instruction. The call
instruction changes the stack pointer, and pop instruction restores its
value. However, the rule for computing CFA is not updated and is wrong on
the pop instruction. So, e.g. backtrace in gdb does not work when on the pop
instruction. This adds cfi instructions for both call and pop instructions.

cfi_adjust_cfa_offset** instruction is used with the appropriate offset for
setting the rules to calculate CFA correctly.

Patch by Violeta Vukobrat.

Differential Revision: http://reviews.llvm.org/D14021

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@252176 91177308-0d34-0410-b5e6-96231b3b80d8