[compiler-rt] [Fuchsia][cmake] Avoid referencing cxx_shared in compiler-rt (PR #112257)

[Louis Dionne via llvm-commits]

https://github.com/ldionne commented:

Does someone understand how the layering works for compiler-rt? Libc++ links against compiler-rt itself, so how can we depend on libc++ from compiler-rt?

https://github.com/llvm/llvm-project/pull/112257