bobcat: Fix build on aarch64-linux

The code base requires a C++20 capable compiler toolchain.

Also, we need to link with the gcc library explicitly to avoid running
into undefined reference to `__aarch64_ldadd4_acq_rel' errors.

pkgs/development/libraries/bobcat/default.nix

@@ -26,6 +26,9 @@ stdenv.mkDerivation rec {
     patchShebangs .
   '';
 
+  # have to link to static gcc lib on aarch64-linux explicitly
+  NIX_LDFLAGS = lib.optionalString (with stdenv.targetPlatform; isAarch64 && isLinux) "-lgcc";
+
   buildPhase = ''
     ./build libraries all
     ./build man

pkgs/top-level/all-packages.nix

@@ -18267,7 +18267,11 @@ with pkgs;
     else callPackage ../os-specific/linux/bionic-prebuilt { };
 
 
-  bobcat = callPackage ../development/libraries/bobcat { };
+  bobcat = callPackage ../development/libraries/bobcat
+    (lib.optionalAttrs (with stdenv.hostPlatform; isAarch64 && isLinux) {
+      # C++20 is required, aarch64-linux has gcc 9 by default
+      stdenv = gcc10Stdenv;
+    });
 
   boehmgc = callPackage ../development/libraries/boehm-gc { };