Rename basic block sections options to be consistent.

D68049 created options for basic block sections: -fbasic-block-sections=,
-funique-basic-block-section-names. Rename options in llc and lld (--lto-)
to be consistent. Specifically,

+ Rename basicblock-sections to basic-block-sections
+ Rename unique-bb-section-names to unique-basic-block-section-names

Differential Revision: https://reviews.llvm.org/D84462