[CMake] Don't use LIBCXXABI_ENABLE_STATIC option before its declared
[CMake] Don't use LIBCXXABI_ENABLE_STATIC option before its declared

Summary:
rL337867 introduced two new cmake_dependent_option options:
- LIBCXXABI_INSTALL_STATIC_LIBRARY
- LIBCXXABI_INSTALL_SHARED_LIBRARY

They depend on LIBCXXABI_ENABLE_STATIC and LIBCXXABI_ENABLE_SHARED
and so therefore need to (it seems) come after the declaration of
these two options.

Subscribers: mgorny, aheejin, christof, ldionne, cfe-commits

Differential Revision: https://reviews.llvm.org/D49825

git-svn-id: 6a9f6578bdee8d959f0ed58970538b4ab6004734@337982 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/libcxxabi,llvm-mirror/libcxxabi,llvm-mirror/libcxxabi,llvm-mirror/libcxxabi,llvm-mirror/libcxxabi