[PowerPC] 32-bit ELF PIC support

This adds initial support for PPC32 ELF PIC (Position Independent Code; the
-fPIC variety), thus rectifying a long-standing deficiency in the PowerPC
backend.

Patch by Justin Hibbits!

llvm-svn: 213427
diff --git a/llvm/test/CodeGen/PowerPC/sections.ll b/llvm/test/CodeGen/PowerPC/sections.ll
index 0ff4a89..d77dfdd 100644
--- a/llvm/test/CodeGen/PowerPC/sections.ll
+++ b/llvm/test/CodeGen/PowerPC/sections.ll
@@ -1,8 +1,12 @@
 ; Test to make sure that bss sections are printed with '.section' directive.
 ; RUN: llc < %s -mtriple=powerpc-unknown-linux-gnu | FileCheck %s
+; RUN: llc < %s -mtriple=powerpc-unknown-linux-gnu -relocation-model=pic | FileCheck %s -check-prefix=PIC
 
 @A = global i32 0
 
 ; CHECK:  .section  .bss,"aw",@nobits
 ; CHECK:  .globl A
 
+; PIC:    .section  .got2,"aw",@progbits
+; PIC:    .section  .bss,"aw",@nobits
+; PIC:    .globl A