Move macOS TMPDIR hack from initNix to initLibStore

This code is bad. We shouldn't unset variables in programs whose
children may need them. Fixing one issue at a time, so postponing.
See https://github.com/NixOS/nix/issues/7731

Part of an effort to make it easier to initialize the right things,
by moving code into the appropriate libraries.

src/libmain/shared.cc

@@ -169,14 +169,6 @@ void initNix()
     gettimeofday(&tv, 0);
     srandom(tv.tv_usec);
 
-    /* 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 (hasPrefix(getEnv("TMPDIR").value_or("/tmp"), "/var/folders/"))
-        unsetenv("TMPDIR");
-#endif
-
 }
 
 

src/libstore/globals.cc

@@ -343,6 +343,14 @@ void initLibStore() {
 
     preloadNSS();
 
+    /* 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 (hasPrefix(getEnv("TMPDIR").value_or("/tmp"), "/var/folders/"))
+        unsetenv("TMPDIR");
+#endif
+
     initLibStoreDone = true;
 }