build: [gn] use clang and custom stdlib when building node on linux

build/node/BUILD.gn

@@ -72,6 +72,9 @@ action("gyp_node") {
     # This has _gn suffixed otherwise it gets overridden by a shlib_suffix
     # that's set in node's gyp files. Don't ask me 🤷
     "-D", "shlib_suffix_gn=" + shlib_suffix,
+    "-D", "llvm_dir=" + rebase_path("//third_party/llvm-build/Release+Asserts"),
+    "-D", "libcxx_dir=" + rebase_path("//buildtools/third_party/libc++"),
+    "-D", "libcxxabi_dir=" + rebase_path("//buildtools/third_party/libc++abi"),
     "-Goutput_dir=./$target_out_dir", # bizarrely, gyp generates from the build root instead of from cwd
     "-fninja",
     rebase_path("//third_party/electron_node/node.gyp", root_build_dir),

build/node/node_override.gypi

@@ -6,6 +6,34 @@
 
     'shlib_suffix': '<(shlib_suffix_gn)',
   },
+  'conditions': [
+    ['OS=="linux"', {
+      'make_global_settings': [
+        ['CC', '<(llvm_dir)/bin/clang'],
+        ['CXX', '<(llvm_dir)/bin/clang++'],
+        ['CC.host', '$(CC)'],
+        ['CXX.host', '$(CXX)'],
+      ],
+      'target_defaults': {
+        'target_conditions': [
+          ['_toolset=="target"', {
+            'cflags_cc': [
+              '-std=gnu++14',
+              '-nostdinc++',
+              '-isystem<(libcxx_dir)/trunk/include',
+              '-isystem<(libcxxabi_dir)/trunk/include',
+            ],
+            'ldflags': [
+              '-nostdlib++',
+            ],
+            'libraries': [
+              '../../../../../../libc++.so',
+            ],
+          }]
+        ]
+      }
+    }]
+  ],
   'target_defaults': {
     'target_conditions': [
       ['_target_name=="node_lib"', {