* core: Make platform environment an instance not class method
In preparation for accessing data constructed in __init__.
* macos: set consistent macosx deployment target
This should silence numerous warnings from mixed gcc/macos toolchains.
* perl: prevent too-new deployment target version
```
*** Unexpected MACOSX_DEPLOYMENT_TARGET=11
***
*** Please either set it to a valid macOS version number (e.g., 10.15) or to empty.
```
* Stylin'
* Add deployment target overrides to failing autoconf packages
* Move configure workaround to base autoconf package
This reverts commit 3c119eaf8b4fb37c943d503beacf5ad2aa513d4c.
* Stylin'
* macos: add utility functions for SDK
These aren't yet used but should probably be added to spack debug
report.
2fa6cd6d23