Move c++ configs from buildtools to build/config/c++ [src-side change]

build/config/c++/BUILD.gn

Index: build/config/c++/BUILD.gn
diff --git a/build/config/c++/BUILD.gn b/build/config/c++/BUILD.gn
index baad310d724d423cada78d237f0f06b2607b2985..0f594984b21e2c3fd771f52eaedb9358cbd742e0 100644
--- a/build/config/c++/BUILD.gn
+++ b/build/config/c++/BUILD.gn
@@ -19,5 +19,38 @@ config("c++flags") {
       "-isystem" + rebase_path("$prefix/libc++/$include", root_build_dir),
       "-isystem" + rebase_path("$prefix/libc++abi/$include", root_build_dir),
     ]
+    if (is_linux && current_cpu == "arm") {
+      cflags_c = [ "-isystem" +
+                   rebase_path("$prefix/libunwind/$include", root_build_dir) ]
+      cflags_cc += [ "-isystem" +
+                     rebase_path("$prefix/libunwind/$include", root_build_dir) ]
+    }
+
+    # Make sure we don't link against libc++ or libstdc++.
+    ldflags = [ "-nodefaultlibs" ]
+
+    # Unfortunately, there's no way to disable linking against just
+    # libc++ (besides using clang instead of clang++); -nodefaultlibs
+    # removes all of the default libraries, so add back the ones that we
+    # need.
+    libs = [
+      "c",
+      "m",
+    ]
+
+    if (!is_mac) {
+      libs += [
+        "gcc_s",
+        "rt",
+      ]
+    }
+
+    if (is_mac && using_sanitizer) {
+      lib_dirs = [ "//third_party/llvm-build/Release+Asserts/lib/clang/$clang_version/lib/darwin" ]
+
+      if (is_asan) {
+        libs += [ "clang_rt.asan_osx_dynamic" ]
+      }
+    }
   }
 }