[CMake] Set the default ABI version for Fuchsia in CMake as well

This is neeeded since the CMake value is used for the SOVERSION.

Differential Revision: https://reviews.llvm.org/D45529

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@329983 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed