Add/change lots of stuff in std

[kylewlacy]

This PR makes a ton of little changes to the std package, including some minor ergonomics tweaks, toolchain cleanups, and some new features:

• Update the pack_tools bundle (required to due to upstream changes for resources)
  • [Breaking] Overhaul resource handling to avoid extra copying brioche#42
  • [Breaking] Implement support for resolving transitive dependencies in dynamic libraries brioche#43
  • [Breaking] More changes to pack tools brioche#44
  • Even more resource tweaks brioche#45
• Changes to std.tools() / std.toolchain()
  • Fix stray Perl modules getting put in the root of std.toolchain()
  • Fix util-linux stuff getting put under usr/ in std.toolchain()
  • Disable locales when building bc in std.tools() to save some space
  • Add which to std.tools()
  • Add patchelf to std.toolchain()
  • Add bin/cc -> bin/gcc symlink in std.toolchain()
  • Tweak glibc build to separate build and autowrap
  • Set $MAGIC / $LIBRARY_PATH / $PKG_CONFIG_PATH when using std.tools() / std.toolchain() as dependencies
• Add std.autowrap() to auto-wrap external binaries
• Add std.setEnv() to set env vars when an artifact gets used as a dependencies
• Add std.withRunnableLink() to set a symlink for use with brioche-run
• Add std.bashRunnable to make a runnable Bash script (for use with brioche-run)
• Clean up methods on std.Process
• Export std.workDir and std.homeDir (for use with std.tpl)