ocaml: fix build w/glibc-2.34

ChangeLog: https://hydra.nixos.org/build/154122673

pkgs/development/compilers/ocaml/4.12.nix

@@ -3,4 +3,9 @@ import ./generic.nix {
   minor_version = "12";
   patch_version = "0";
   sha256 = "1hxy349jfa2vkfgmxf6pvd9w4z5bmcgsg0fxfdabcghyvjw9vvir";
+  patches = [
+    { url = "https://src.fedoraproject.org/rpms/ocaml/raw/129153b85109944bf0b2922949f77ef8f32b39a1/f/0004-Dynamically-allocate-the-alternate-signal-stack-1026.patch";
+      sha256 = "sha256-FdQ1HkMKHU9QvgLPUBvMdPiEa7w7IL3+1F3SLv63Gog=";
+    }
+  ];
 }

pkgs/development/compilers/ocaml/generic.nix

@@ -1,4 +1,4 @@
-{ minor_version, major_version, patch_version
+{ minor_version, major_version, patch_version, patches ? []
 , ...}@args:
 let
   versionNoPatch = "${toString major_version}.${toString minor_version}";
@@ -6,7 +6,7 @@ let
   safeX11 = stdenv: !(stdenv.isAarch32 || stdenv.isMips || stdenv.hostPlatform.isStatic);
 in
 
-{ lib, stdenv, fetchurl, ncurses, buildEnv, libunwind
+{ lib, stdenv, fetchurl, ncurses, buildEnv, libunwind, fetchpatch
 , libX11, xorgproto, useX11 ? safeX11 stdenv && !lib.versionAtLeast version "4.09"
 , aflSupport ? false
 , flambdaSupport ? false
@@ -44,6 +44,8 @@ stdenv.mkDerivation (args // {
 
   inherit src;
 
+  patches = map fetchpatch patches;
+
   strictDeps = true;
 
   prefixKey = "-prefix ";