Merge changes Icf26010a,Ib6161567 into main

* changes:
  Always initialize curl in parent process on darwin
  Fix failing darwin tests

src/libstore/globals.cc

@@ -25,6 +25,7 @@
 #include "config-impl.hh"
 
 #ifdef __APPLE__
+#include <curl/curl.h>
 #include <sys/sysctl.h>
 #endif
 
@@ -409,10 +410,21 @@ void initLibStore() {
 
     preloadNSS();
 
+#if __APPLE__
+    /* Because of an objc quirk[1], calling curl_global_init for the first time
+       after fork() will always result in a crash.
+       Up until now the solution has been to set OBJC_DISABLE_INITIALIZE_FORK_SAFETY
+       for every nix process to ignore that error.
+       Instead of working around that error we address it at the core -
+       by calling curl_global_init here, which should mean curl will already
+       have been initialized by the time we try to do so in a forked process.
+
+       [1] https://github.com/apple-oss-distributions/objc4/blob/01edf1705fbc3ff78a423cd21e03dfc21eb4d780/runtime/objc-initialize.mm#L614-L636
+    */
+    curl_global_init(CURL_GLOBAL_ALL);
     /* On macOS, don't use the per-session TMPDIR (as set e.g. by
        sshd). This breaks build users because they don't have access
        to the TMPDIR, in particular in ‘nix-store --serve’. */
-#if __APPLE__
     if (getEnv("TMPDIR").value_or("/tmp").starts_with("/var/folders/"))
         unsetenv("TMPDIR");
 #endif