[AIX][XCOFF] Output XCOFF object text section header and symbol entry for program code.

SUMMARY
Original form of this patch is provided by Stefan Pintillie.

The patch try to output program code section header , symbol entry for program code (PR) and Instruction into the raw text section.
The patch include how to alignment and layout the CSection in the text section.
The patch also reorganize the code , put some codes into a function(XCOFFObjectWriter::writeSymbolTableEntryForControlSection)
Additional: We can not add raw data of text section test in the patch, If want to output raw text section data,it need a function description patch first.

Reviewers: hubert.reinterpretcast, sfertile, jasonliu, xingxue.
Subscribers: wuzish, nemanjai, hiraditya, MaskRay, jsjji.

Differential Revision: https://reviews.llvm.org/D66969

llvm-svn: 374914

Author: Digger Lin

llvm/test/CodeGen/PowerPC/aix-return55.ll

@@ -0,0 +1,11 @@
+; RUN: llc -mcpu=pwr9 -mtriple=powerpc-ibm-aix-xcoff -verify-machineinstrs < %s | FileCheck %s
+
+
+define dso_local signext i32 @foo() {
+entry:
+  ret i32 55
+; CHECK-LABEL: .foo:
+; CHECK: li 3, 55
+; CHECK: blr
+}
+