[NFC][libcxx] Remove trailing whitespace

It's incredibly annoying when trying to create diffs

llvm-svn: 361981
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: a2a1ec27d0e799725cdd41f8456deb9a49433e2d
18 files changed