tsan: fix cur_thread alignment

Commit 354ded67 ("tsan: align ThreadState to cache line")
did an incomplete thing. It marked ThreadState as cache line
aligned, but the thread local ThreadState instance is declared
as an aligned char array with hard-coded 64-byte alignment.
On PowerPC cache line size is 128 bytes, so the hard-coded
64-byte alignment is not enough.
Use cache line alignment consistently.

Differential Revision: https://reviews.llvm.org/D110629