Corrosion does not forward the `CMAKE_OSX_DEPLOYMENT_TARGET` to cargo.
As a result we end up building the Rust-libraries for the default target,
which is usually current macOS-version. But CMake links using the set
target, so we link for a version older than we built for.
To properly build for older macOS versions, the env variable
`MACOSX_DEPLOYMENT_TARGET` should instead be set, which cargo,
cmake and friends read by default. This can then lead to
warnings if you have libraries (e.g. PCRE2) built for newer
than our minimum version. Therefore we do not set a min-target
by default.
fish wants to build with -mmacosx-version-min=10.9. This is important
because it ensures that we do not use functions or linker features which
which are not available on 10.9. However this collides with the fact
that fish also prefers to use a pcre2 package installed on the system,
which is typically built for that system.
Mac ld will (rightly) complain when it sees a 10.9-targeted binary
linking a 10.15-targeted dylib. This is an annoying warning that gets
emitted on every build.
We could fix this either having Mac builds prefer the vendored PCRE2
by default, or by having debug builds target the system version. But
we want to continue to default to system PCRE2 and we don't want to risk
losing compatibility with older Mac versions. So we will just suppress
all linker warnings in Mac debug builds.
Building on OS X versions prior to 10.13.6 fails at the very end when
running `codesign`.
The `-options runtime`-argument isn't available on these earlier
versions of the OS.
Simply running codesign without that argument (on OS X <10.13.6) seems
to produce a runnable binary with no security warnings.
