libserdes: fix build with avro-cpp 1.12.0

Some finagling is required to make the configure scripts cooperate with the required
bump to the minimum C++ standard version. avro-cpp needs at least C++17, but libserdes
is stuck at C++11.

pkgs/by-name/li/libserdes/package.nix

@@ -4,7 +4,6 @@
   fetchFromGitHub,
   perl,
   which,
-  boost,
   rdkafka,
   jansson,
   curl,
@@ -35,7 +34,6 @@ stdenv.mkDerivation rec {
   ];
 
   buildInputs = [
-    boost
     rdkafka
     jansson
     curl
@@ -43,10 +41,26 @@ stdenv.mkDerivation rec {
     avro-cpp
   ];
 
-  makeFlags = [ "GEN_PKG_CONFIG=y" ];
+  configureFlags = [
+    # avro-cpp public headers use at least C++17 features, but libserdes configure scripts
+    # basically cap it at C++11. It's really unfortunate that we have to patch the configure scripts for this,
+    # but this seems to be the most sensible way.
+    # - NIX_CFLAGS_COMPILE - fails because of -Werror in compiler checks since --std=... has no effect for C compilers.
+    # - CXXFLAGS without patching configure.self does nothing, because --std=c++11 is appended to the final flags, overriding
+    #   everything specified manually.
+    "--CXXFLAGS=${toString [ "--std=c++17" ]}"
+  ];
+
+  makeFlags = [
+    "GEN_PKG_CONFIG=y"
+  ];
 
   postPatch = ''
     patchShebangs configure lds-gen.pl
+    # Don't append the standard to CXXFLAGS, since we want to set it higher for avro-cpp.
+    substituteInPlace configure.self --replace-fail \
+      'mkl_mkvar_append CXXFLAGS CXXFLAGS "--std=c++11"' \
+      ":" # Do nothing, we set the standard ourselves.
   '';
 
   # Has a configure script but it’s not Autoconf so steal some bits from multiple-outputs.sh: