fix(3p/nix): Link to glog built by Nix

Same as cl/921, it seems that the trick to making this work is indeed
overriding the C++ standard used in the dependency.

Change-Id: I3c5984d71014d774c161ecc283844f504fd44719
Reviewed-on: https://cl.tvl.fyi/c/depot/+/922
Tested-by: BuildkiteCI
Reviewed-by: lukegb <lukegb@tvl.fyi>

third_party/glog/default.nix

@@ -7,7 +7,10 @@ in llvmPackages.libcxxStdenv.mkDerivation {
   src = ./.;
 
   nativeBuildInputs = [ cmake ];
-  cmakeFlags = [ "-WITH_GFLAGS=OFF" ];
+  cmakeFlags = [
+    "-DCMAKE_CXX_STANDARD=17"
+    "-WITH_GFLAGS=OFF"
+  ];
 
   meta = with lib; {
     homepage = "https://github.com/google/glog";

third_party/nix/CMakeLists.txt

@@ -17,16 +17,11 @@ set(PKGCONFIG_INSTALL_DIR ${CMAKE_INSTALL_LIBDIR}/pkgconfig)
 find_package(BZip2)
 find_package(Boost COMPONENTS context) # probably coroutine + ::headers, lets find out
 find_package(CURL)
+find_package(LibLZMA)
 find_package(SQLite3)
 find_package(Threads)
-find_package(LibLZMA)
 find_package(absl REQUIRED)
-
-# Linking precompiled glog binaries (linked against libstdc++) leads
-# to working binaries that do not output log messages. It seems that
-# in order to use glog with LLVM & libc++, one needs to make glog a
-# part of the local project build.
-add_subdirectory(glog)
+find_package(glog REQUIRED)
 
 # generate a configuration file (autoheader-style) to configure
 # certain symbols that Nix depends on.

third_party/nix/default.nix

@@ -17,11 +17,6 @@ in pkgs.llvmPackages.libcxxStdenv.mkDerivation {
   version = "2.3.4";
   src = ./.;
 
-  # Abseil's sources need to be symlinked into Nix' sources.
-  postUnpack = ''
-    ln -fs ${pkgs.glog.drvAttrs.src} nix/glog
-  '';
-
   nativeBuildInputs = with pkgs; [
     bison
     clang-tools
@@ -41,6 +36,7 @@ in pkgs.llvmPackages.libcxxStdenv.mkDerivation {
     curl
     editline
     flex
+    glog
     libseccomp
     libsodium
     openssl

third_party/nix/glog

@@ -1 +0,0 @@
-../glog/