[PPC64LE] Add a V2 abi test case for toc-relative access.

[sfertile]

Summary

The relocations for the toc-relative access sequence already work due to the existing V1 ABI work. This patch adds a V2 abi specific test for coverage.

This patch has a dependency on https://reviews.llvm.org/D44483

[sfertile]

fixed spelling mistake.

[ruiu]

LGTM

test/ELF/ppc64le-toc-rel.s

+# REQUIRES: ppc
+# RUN: llvm-mc -filetype=obj -triple=powerpc64le-unknown-linux %s -o %t.o
+# RUN: llvm-readobj -relocations %t.o | FileCheck -check-prefix=RELOCS %s
+# RUN: ld.lld %t.o -o %t2
+# RUN: llvm-objdump -D %t2 | FileCheck %s
+
+# Make sure we calculate the offset correctly for a toc-relative access to a
+# global variable as described by the PPC64 Elf V2 abi.
+.abiversion 2
+
+#  int global_a = 55
+   .globl      global_a
+   .section    ".data"
+   .align      2
+   .type       global_a, @object
+   .size       global_a, 4
+   .p2align    2
+global_a:
+   .long   41
+
+
+   .section        ".text"
+   .align 2
+   .global _start
+   .type   _start, @function
+_start:
+.Lfunc_gep0:
+    addis 2, 12, .TOC.-.Lfunc_gep0@ha
+    addi 2, 2, .TOC.-.Lfunc_gep0@l
+.Lfunc_lep0:
+    .localentry _start, .Lfunc_lep0-.Lfunc_gep0
+
+    addis 3, 2, global_a@toc@ha
+    addi 3, 3, global_a@toc@l
+    li 0,1
+    lwa 3, 0(3)
+    sc
+.size   _start,.-_start
+
+# Verify the relocations that get emitted for the global variable are the
+# expected ones.
+# RELOCS:      Relocations [
+# RELOCS-NEXT:   .rela.text {
+# RELOCS:          0x8 R_PPC64_TOC16_HA global_a 0x0
+# RELOCS:          0xC R_PPC64_TOC16_LO global_a 0x0
+
+# Want to check _start for the values used to build the offset from the TOC base
+# to global_a. The .TOC. symbol is expected at address 0x10030000, and the
+# TOC base is address-of(.TOC.) + 0x8000.  The expected offset is:
+# 0x10020000(global_a) - 0x10038000(Toc base) = -0x18000(Offset)
+# which gets materialized into r3 as ((-1 << 16) - 32768).
+
+# CHECK:      Disassembly of section .text:
+# CHECK-NEXT: _start:
+# CHECK:      10010008:       ff ff 62 3c     addis 3, 2, -1
+# CHECK-NEXT: 1001000c:       00 80 63 38     addi 3, 3, -32768
+
+# CHECK:      Disassembly of section .data:
+# CHECK-NEXT: global_a:
+# CHECK-NEXT: 10020000:       29 00 00 00
+
+# CHECK:      Disassembly of section .got:
+# CHECK-NEXT: .got:
+# CHECK-NEXT: 10030000:       00 80 03 10