fix(3p/nix): propagate dependencies which are needed by people linking in nix

This includes absl, which we install into the output, and boost and the boehm GC,
which are moved to propagated deps.

Change-Id: I8f9f9795ff92e26b2320359064241d7fd59c2d33
Reviewed-on: https://cl.tvl.fyi/c/depot/+/549
Reviewed-by: tazjin <mail@tazj.in>

third_party/default.nix

@@ -92,6 +92,7 @@ let
       mdbook
       meson
       mime-types
+      mkShell
       moreutils
       nano
       nginx

third_party/nix/CMakeLists.txt

@@ -30,6 +30,14 @@ find_package(LibLZMA)
 # builds this symlink is automatically replaced with an appropriate
 # link to the Abseil sources in the Nix store.
 add_subdirectory(abseil_cpp)
+install(DIRECTORY abseil_cpp/absl
+  DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
+  FILES_MATCHING
+    PATTERN "*.inc"
+    PATTERN "*.h"
+    PATTERN "copts" EXCLUDE
+    PATTERN "testdata" EXCLUDE
+  )
 
 # Linking precompiled glog binaries (linked against libstdc++) leads
 # to working binaries that do not output log messages. It seems that

third_party/nix/default.nix

@@ -36,13 +36,11 @@ in pkgs.llvmPackages.libcxxStdenv.mkDerivation {
  # TODO(tazjin): Some of these might only be required for native inputs
   buildInputs = with pkgs; [
     aws-s3-cpp
-    boost
     brotli
     bzip2
     curl
     editline
     flex
-    largeBoehm
     libseccomp
     libsodium
     openssl
@@ -50,6 +48,11 @@ in pkgs.llvmPackages.libcxxStdenv.mkDerivation {
     xz
   ];
 
+  propagatedBuildInputs = with pkgs; [
+    boost
+    largeBoehm
+  ];
+
   # Install the various symlinks to the Nix binary which users expect
   # to exist.
   postInstall = ''