Use the integrated assembler as default on SystemZ

Use the integrated assembler as default on SystemZ

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 deliberately using an invalid instruction in
inline asm now have to use -no-integrated-as.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225820 91177308-0d34-0410-b5e6-96231b3b80d8