lean -R
This PR skips attempting to compute a module name from the file name and root directory (i.e., `lean -R`) if a name is already provided via `lean --setup`. This is accomplished by porting the rest of the frontend code in the `try` block to Lean.
LEAN_EXPORT
CMAKE_CXX_SYSROOT_FLAG
bool operator==(data_value const & a, data_value const & b)
IO.FS.realPath