Use the integrated assembler as default on PowerPC

Use the integrated assembler as default on PowerPC

This was already done in clang, this commit now uses the integrated
assembler as default when using LLVM tools directly.

A number of test cases using inline asm had to be adapted, either by
updating the expected output, or by using -no-integrated-as (for such
tests that deliberately use an invalid instruction in inline asm).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225819 91177308-0d34-0410-b5e6-96231b3b80d8