linkage_checker: report linkage with system frameworks

[carlocab]

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Currently, brew linkage reports linkage with system frameworks only if
they can be found on the file system. This results in this linkage not
being reported on Big Sur and newer, where system libraries are stored
in the dyld cache instead.

Let's fix that by avoiding silently ignoring system frameworks by moving
them out of #harmless_broken_link?. We retain the behaviour desired
from 7228e60 by deferring checking if a
broken library is actually a system framework to just before we add it
to @broken_dylibs.

To see how this changes the behaviour of brew linkage, here's an
example with this change:

❯ brew linkage neovim
System libraries:
  /System/Library/Frameworks/CoreServices.framework/Versions/A/CoreServices
  /usr/lib/libSystem.B.dylib
  /usr/lib/libiconv.2.dylib
  /usr/lib/libutil.dylib
Homebrew libraries:
  /usr/local/opt/gettext/lib/libintl.8.dylib (gettext)
  /usr/local/opt/libtermkey/lib/libtermkey.1.dylib (libtermkey)
  /usr/local/opt/libuv/lib/libuv.1.dylib (libuv)
  /usr/local/opt/luajit/lib/libluajit-5.1.2.dylib (luajit)
  /usr/local/opt/luv/lib/libluv.1.dylib (luv)
  /usr/local/opt/msgpack/lib/libmsgpackc.2.dylib (msgpack)
  /usr/local/opt/tree-sitter/lib/libtree-sitter.0.dylib (tree-sitter)
  /usr/local/opt/unibilium/lib/libunibilium.4.dylib (unibilium)

and without this change:

❯ brew linkage neovim
System libraries:
  /usr/lib/libSystem.B.dylib
  /usr/lib/libiconv.2.dylib
  /usr/lib/libutil.dylib
Homebrew libraries:
  /usr/local/opt/gettext/lib/libintl.8.dylib (gettext)
  /usr/local/opt/libtermkey/lib/libtermkey.1.dylib (libtermkey)
  /usr/local/opt/libuv/lib/libuv.1.dylib (libuv)
  /usr/local/opt/luajit/lib/libluajit-5.1.2.dylib (luajit)
  /usr/local/opt/luv/lib/libluv.1.dylib (luv)
  /usr/local/opt/msgpack/lib/libmsgpackc.2.dylib (msgpack)
  /usr/local/opt/tree-sitter/lib/libtree-sitter.0.dylib (tree-sitter)
  /usr/local/opt/unibilium/lib/libunibilium.4.dylib (unibilium)

[BrewTestBot]

Review period will end on 2022-07-19 at 04:05:57 UTC.

[Bo98]

I'm not sure I understand the scenario presented in the original issue. It seems like the desire was to ship binaries built on older macOS versions linked with frameworks that only exist on newer macOS versions. Why?

[carlocab]

I'm not sure I understand the scenario presented in the original issue. It seems like the desire was to ship binaries built on older macOS versions linked with frameworks that only exist on newer macOS versions. Why?

This is not clear to me either. Maybe @fxcoudert remembers?

[fxcoudert]

Nope, do not remember, sorry.

[BrewTestBot]

Review period ended.