Is xdebug broken on darwin?

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I’m using nixpkgs for the first time, investigating setting up development environments with it for PHP and JavaScript.

The following shell.nix works fine on linux:

{ pkgs ? import (fetchTarball "https://github.com/NixOS/nixpkgs/archive/nixos-20.09.tar.gz") {} }:

pkgs.mkShell {
  buildInputs = [
    pkgs.phpExtensions.xdebug
  ];
}

However, the following fails on darwin:

{ pkgs ? import (fetchTarball "https://github.com/NixOS/nixpkgs/archive/nixpkgs-20.09-darwin.tar.gz") {} }:

pkgs.mkShell {
  buildInputs = [
    pkgs.phpExtensions.xdebug
  ];
}

❯ nix-shell
these derivations will be built:
  /nix/store/dihidkjlcpxhl9wnckg9n4ml7dm39m8v-php-xdebug-2.8.1.drv
building '/nix/store/dihidkjlcpxhl9wnckg9n4ml7dm39m8v-php-xdebug-2.8.1.drv'...
unpacking sources
unpacking source archive /nix/store/pzwvqf8db5q5wwan94fc2yqq13q1x8zi-xdebug-2.8.1.tgz
source root is xdebug-2.8.1
setting SOURCE_DATE_EPOCH to timestamp 1575046449 of file xdebug-2.8.1/xdebug_xml.h
patching sources
autoreconfPhase
Configuring for:
PHP Api Version:         20190902
Zend Module Api No:      20190902
Zend Extension Api No:   320190902
configuring
fixing libtool script ./build/ltmain.sh
configure flags: --disable-static --prefix=/nix/store/wbjhi6f0a8i0wfzrsw2m1106dn4qmpf9-php-xdebug-2.8.1
checking for grep that handles long lines and -e... /nix/store/x9qcs609bqn68i26l8i4z6qq3hsqi5vf-gnugrep-3.4/bin/grep
checking for egrep... /nix/store/x9qcs609bqn68i26l8i4z6qq3hsqi5vf-gnugrep-3.4/bin/grep -E
checking for a sed that does not truncate output... /nix/store/mcz107ij67iidr86mm74sh98q193y7mq-gnused-4.8/bin/sed
checking for pkg-config... no
checking whether the C compiler works... no
configure: error: in `/private/tmp/nix-build-php-xdebug-2.8.1.drv-0/xdebug-2.8.1':
configure: error: C compiler cannot create executables
See `config.log' for more details
builder for '/nix/store/dihidkjlcpxhl9wnckg9n4ml7dm39m8v-php-xdebug-2.8.1.drv' failed with exit code 77
error: build of '/nix/store/dihidkjlcpxhl9wnckg9n4ml7dm39m8v-php-xdebug-2.8.1.drv' failed

Since I’m using the stable channel, I assumed either xdebug would build successfully, or it wouldn’t be in the package tree at all. Any suggestions?