* relocate: call install_name_tool less
* zstd: fix race condition
Multiple times on my mac, trying to install in parallel led to failures
from multiple tasks trying to simultaneously create `$PREFIX/lib`.
* PackageMeta: simplify callback flush
* Relocate: use spack.platforms instead of platform
* Relocate: code improvements
* fix zstd
* Automatically fix rpaths for packages on macOS
* Only change library IDs when the path is already in the rpath
This restores the hardcoded library path for GCC.
* Delete nonexistent rpaths and add more testing
* Relocate: Allow @executable_path and @loader_path
c48b733773