[compiler-rt] [compiler-rt][cmake] Add option to control shared library builds (PR #139042)

[Derek Schuff via llvm-commits]

dschuff wrote:

I feel like there must already be some kind of option to control whether shared or static libs are built. Maybe this is a question for a runtimes expert like @petrhosek 

https://github.com/llvm/llvm-project/pull/139042