[AIX] discard the label in the csect of function description and use qualname for linkage

SUMMARY:

SUMMARY
for a source file  "test.c"

void foo() {};

llc will generate assembly code as (assembly patch)
     .globl  foo
     .globl  .foo
     .csect foo[DS]
foo:

        .long   .foo
        .long   TOC[TC0]
        .long   0

   and symbol table as (xcoff object file)
   [4]     m   0x00000004     .data     1  unamex                    foo
   [5]     a4  0x0000000c       0    0     SD       DS    0    0
   [6]     m   0x00000004     .data     1  extern                    foo
   [7]     a4  0x00000004       0    0     LD       DS    0    0

   After first patch, the assembly will be as

        .globl  foo[DS]                 # -- Begin function foo
        .globl  .foo
        .align  2
        .csect foo[DS]
        .long   .foo
        .long   TOC[TC0]
        .long   0

    and symbol table will as
   [6]     m   0x00000004     .data     1  extern                    foo
   [7]     a4  0x00000004       0    0     DS      DS    0    0
Change the code for the assembly path and xcoff objectfile patch for llc.

Reviewers: Jason Liu
Subscribers: wuzish, nemanjai, hiraditya

Differential Revision: https://reviews.llvm.org/D76162