Add options for separate compile and link sysroots
Add CMAKE_SYSROOT_COMPILE and CMAKE_SYSROOT_LINK variables to as
operation-specific alternatives to CMAKE_SYSROOT. This will be useful
for Android NDKs that compile and link with different sysroot values
(e.g. r14 with unified headers).
Co-Author: @Orphis
Issue: #16584 (closed)