White space fix.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214455 91177308-0d34-0410-b5e6-96231b3b80d8
X86 MC: Reject invalid segment registers before a memory operand colon

Previously we would execute unreachable during object emission.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214456 91177308-0d34-0410-b5e6-96231b3b80d8
X86 MC: Don't crash on empty memory operand parens

Instead, create an absolute memory operand.

Fixes PR20504.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214457 91177308-0d34-0410-b5e6-96231b3b80d8