[OpenEmbedded] Fix lib paths for OpenEmbedded targets

Summary:
The lib paths are not correctly picked up for OpenEmbedded sysroots (like arm-oe-linux-gnueabi) for 2 reasons:

1. OpenEmbedded sysroots are of the form <sysroot>/usr/lib/<triple>/x.y.z. This form is handled in clang but only for Freescale vendor.

2. 64-bit OpenEmbedded sysroots may not have a /usr/lib dir. So they cannot find /usr/lib64 as it is referenced as /usr/lib/../lib64 in clang.

This is a follow-up to the llvm patch: D48861

Reviewers: dlj, rengolin, fedor.sergeev, javed.absar, hfinkel, rsmith

Reviewed By: rsmith

Subscribers: rsmith, kristof.beyls, cfe-commits

Differential Revision: https://reviews.llvm.org/D48862

llvm-svn: 338294