Install gcc, lower poetry verbosity

Broke in https://github.com/matrix-org/synapse/pull/16019. This would have been caught
if someone ran 'devenv up' during manual testing of that PR, or better yet, if we had
CI for the nix developer environment.

Switch back to the latest release version, which doesn't have the upstream issue:
https://github.com/cachix/devenv/issues/756

changelog.d/16063.misc

@@ -0,0 +1 @@
+Fix building the nix development environment on MacOS systems.

flake.lock

@@ -8,16 +8,16 @@
         "pre-commit-hooks": "pre-commit-hooks"
       },
       "locked": {
-        "lastModified": 1690534632,
-        "narHash": "sha256-kOXS9x5y17VKliC7wZxyszAYrWdRl1JzggbQl0gyo94=",
+        "lastModified": 1688058187,
+        "narHash": "sha256-ipDcc7qrucpJ0+0eYNlwnE+ISTcq4m03qW+CWUshRXI=",
         "owner": "cachix",
         "repo": "devenv",
-        "rev": "6568e7e485a46bbf32051e4d6347fa1fed8b2f25",
+        "rev": "c8778e3dc30eb9043e218aaa3861d42d4992de77",
         "type": "github"
       },
       "original": {
         "owner": "cachix",
-        "ref": "main",
+        "ref": "v0.6.3",
         "repo": "devenv",
         "type": "github"
       }

flake.nix

@@ -45,7 +45,7 @@
     # Output a development shell for x86_64/aarch64 Linux/Darwin (MacOS).
     systems.url = "github:nix-systems/default";
     # A development environment manager built on Nix. See https://devenv.sh.
-    devenv.url = "github:cachix/devenv/main";
+    devenv.url = "github:cachix/devenv/v0.6.3";
     # Rust toolchain.
     rust-overlay.url = "github:oxalica/rust-overlay";
   };
@@ -90,6 +90,9 @@
                   # The rust-analyzer language server implementation.
                   rust-analyzer
 
+		  # For building any Python bindings to C or Rust code.
+		  gcc
+
                   # Native dependencies for running Synapse.
                   icu
                   libffi
@@ -122,7 +125,7 @@
                 languages.python.poetry.activate.enable = true;
                 # Install all extra Python dependencies; this is needed to run the unit
                 # tests and utilitise all Synapse features.
-                languages.python.poetry.install.arguments = ["--extras all"];
+                languages.python.poetry.install.arguments = ["-v" "--extras all"];
                 # Install the 'matrix-synapse' package from the local checkout.
                 languages.python.poetry.install.installRootPackage = true;