[test] Fix a typo in a test directory name. NFC.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@330695 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/test/Driver/Inputs/mingw_ubuntu_tree/usr/include/c++/4.8/86_64-w64-mingw32/.keep b/test/Driver/Inputs/mingw_ubuntu_tree/usr/include/c++/4.8/x86_64-w64-mingw32/.keep
similarity index 100%
rename from test/Driver/Inputs/mingw_ubuntu_tree/usr/include/c++/4.8/86_64-w64-mingw32/.keep
rename to test/Driver/Inputs/mingw_ubuntu_tree/usr/include/c++/4.8/x86_64-w64-mingw32/.keep