[x32] Handle -m64/-m32 switches by Driver in x32 mode

Summary:
Adding remaining 2 cases handling:
* from x32 to 32 via -m32
* from x32 to 64 via -m64

Test Plan: linux-ld test updated

Reviewers: chandlerc, atanasyan

Subscribers: cfe-commits, zinovy.nis

Differential Revision: http://reviews.llvm.org/D4930