build: use LINK_COMPONENTS for linking LLVMSupport
@sdasgup3 is oncall for MHLO this week Hi @sdasgup3 Can you please review this PR ? Thank you! Closing because commit 11b7c33 addresses the problem.
Without this patch, in-tree builds of LLVM+MHLO fail with the following
message:

```
MhloRngUtils specifies LINK_LIBS LLVMSupport, but LINK_LIBS cannot be used
for LLVM libraries.  Please use LINK_COMPONENTS instead.
```