build openssl without threads to avoid stdatomic

overlay.nix

@@ -177,21 +177,33 @@ extraPkgs // {
     ];
   });
 
-  openssl = prev.openssl.overrideAttrs (o: {
-    # we want to apply
-    # https://patch-diff.githubusercontent.com/raw/openssl/openssl/pull/20273.patch";
-    # which disables overriding the -march cflags to the wrong values,
-    # but openssl is used for bootstrapping so that's easier said than
-    # done. Do it the ugly way..
-    postPatch =
-      o.postPatch
-      + (
-        with final;
-        lib.optionalString (
-          stdenv.buildPlatform != stdenv.hostPlatform
-        ) "\nsed -i.bak 's/linux.*-mips/linux-mops/' Configure\n"
-      );
-  });
+  openssl = prev.openssl.overrideAttrs (o:
+    with final;
+    let cross = stdenv.buildPlatform != stdenv.hostPlatform;
+    in
+      {
+        # we want to apply
+        # https://patch-diff.githubusercontent.com/raw/openssl/openssl/pull/20273.patch";
+        # which disables overriding the -march cflags to the wrong values,
+        # but openssl is used for bootstrapping so that's easier said than
+        # done. Do it the ugly way..
+        postPatch =
+          o.postPatch
+          + (
+            lib.optionalString cross ''
+              sed -i.bak 's/linux.*-mips/linux-mops/' Configure
+            ''
+          );
+        # openssl with threads requires stdatomic which drags in libgcc
+        # as a dependency
+        configureFlags = []
+                         ++ (lib.optional cross "no-threads")
+                         ++ o.configureFlags;
+
+        # don't need or want this bash script
+        postInstall = o.postInstall +
+                      (lib.optionalString cross "rm $bin/bin/c_rehash\n");
+      });
 
   pppBuild = prev.ppp;