nix: test script without glibc locales

glibcLocales is not available e.g. on darwin. This change allows
running various dev tools on darwin, and other theoretical
non-glibc systems.

nix/tools/tests.nix

@@ -3,13 +3,16 @@
 , checkedShellScript
 , devCabalOptions
 , ghc
-, glibcLocales
+, glibcLocales ? null
 , gnugrep
 , hpc-codecov
+, hostPlatform
 , jq
+, lib
 , postgrest
 , python3
 , runtimeShell
+, stdenv
 , weeder
 , withTools
 , yq
@@ -125,9 +128,13 @@ let
         withEnv = postgrest.env;
         withTmpDir = true;
       }
-      ''
+      (
+        # required for `hpc markup` in CI; glibcLocales is not available e.g. on Darwin
+        lib.optionalString (stdenv.isLinux && hostPlatform.libc == "glibc") ''
           export LOCALE_ARCHIVE="${glibcLocales}/lib/locale/locale-archive"
+        '' +
 
+        ''
           # clean up previous coverage reports
           mkdir -p coverage
           rm -rf coverage/*
@@ -185,7 +192,8 @@ let
             echo "file://$(pwd)/coverage/hpc_index.html"
             ${ghc}/bin/hpc report coverage/postgrest.tix "''${_arg_leftovers[@]}"
           fi
-      '';
+        ''
+      );
 
   coverageDraftOverlay =
     checkedShellScript