Use empty() instead of size().
Use empty() instead of size().

`!V.size()` where V is a vector is equivalent to `V.empty()`.

git-svn-id: f6089bf0e6284f307027cef4f64114ee9ebb0424@299501 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lld,llvm-mirror/lld