[VE] Optimize toolchain regression test

Optimize toolchain regression test for VE by removing not a useful test
(-fuse-init-array test) and merge several tests to one test which checks
default behavior of driver.  Also add sysroot to reduce conflicts.

These are suggested in https://reviews.llvm.org/D92996.
Thank you so much.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D93084