ci: Use tsan-instrumented cap'n proto in sanitizers job

This makes libmultiprocess CI output match bitcoin core CI output and catches a
race in the new thread busy test from 1238170
(bitcoin-core#214).

Author: ryanofsky

ci/configs/sanitize.bash

@@ -1,6 +1,6 @@
 CI_DESC="CI job running ThreadSanitizer"
 CI_DIR=build-sanitize
-NIX_ARGS=(--arg enableLibcxx true --argstr libcxxSanitizers "Thread")
+NIX_ARGS=(--arg enableLibcxx true --argstr libcxxSanitizers "Thread" --argstr capnprotoSanitizers "thread")
 export CXX=clang++
 export CXXFLAGS="-ggdb -Werror -Wall -Wextra -Wpedantic -Wthread-safety -Wno-unused-parameter -fsanitize=thread"
 CMAKE_ARGS=()

shell.nix

@@ -3,6 +3,7 @@
 , enableLibcxx ? false # Whether to use libc++ toolchain and libraries instead of libstdc++
 , minimal ? false # Whether to create minimal shell without extra tools (faster when cross compiling)
 , capnprotoVersion ? null
+, capnprotoSanitizers ? null # Optional sanitizers to build cap'n proto with
 , cmakeVersion ? null
 , libcxxSanitizers ? null # Optional LLVM_USE_SANITIZER value to use for libc++, see https://llvm.org/docs/CMake.html
 }:
@@ -41,7 +42,17 @@ let
   } // (lib.optionalAttrs (lib.versionOlder capnprotoVersion "0.10") {
     env = { }; # Drop -std=c++20 flag forced by nixpkgs
   }));
-  capnproto = capnprotoBase.override (lib.optionalAttrs enableLibcxx { clangStdenv = llvm.libcxxStdenv; });
+  capnproto = (capnprotoBase.overrideAttrs (old: lib.optionalAttrs (capnprotoSanitizers != null) {
+    env = (old.env or { }) // {
+      CXXFLAGS =
+        lib.concatStringsSep " " [
+          (old.env.CXXFLAGS or "")
+          "-fsanitize=${capnprotoSanitizers}"
+          "-fno-omit-frame-pointer"
+          "-g"
+        ];
+    };
+  })).override (lib.optionalAttrs enableLibcxx { clangStdenv = llvm.libcxxStdenv; });
   clang = if enableLibcxx then llvm.libcxxClang else llvm.clang;
   clang-tools = llvm.clang-tools.override { inherit enableLibcxx; };
   cmakeHashes = {