Handle typeof() expressions

Before this patch, LLDB was not able to evaluate expressions that
resulted in a value with a typeof- or decltype-type. This patch fixes
that.

Before:
  (lldb) p int i; __typeof__(i) j = 1; j
  (typeof (i)) $0 =

After:
  (lldb) p int i; __typeof__(i) j = 1; j
  (typeof (i)) $0 = 1

Differential revision: https://reviews.llvm.org/D43471

rdar://37461520

llvm-svn: 325568