Reland "Roll src/buildtools/third_party/libc++/trunk/ 8fa879467..79a2e924d (426 commits)"

https://chromium-review.googlesource.com/c/chromium/src/+/2988699

BUILD.gn

@@ -1404,7 +1404,8 @@ dist_zip("hunspell_dictionaries_zip") {
 }
 
 copy("libcxx_headers") {
-  sources = libcxx_headers + libcxx_licenses
+  sources = libcxx_headers + libcxx_licenses +
+            [ "//buildtools/third_party/libc++/__config_site" ]
   outputs = [ "$target_gen_dir/electron_libcxx_include/{{source_root_relative_dir}}/{{source_file_part}}" ]
 }
 

script/nan-spec-runner.js

@@ -38,7 +38,7 @@ async function main () {
   const cxxflags = [
     '-std=c++14',
     '-nostdinc++',
-    '-D_LIBCPP_HAS_NO_VENDOR_AVAILABILITY_ANNOTATIONS', // needed by next line
+    `-isystem"${path.resolve(BASE, 'buildtools', 'third_party', 'libc++')}"`,
     `-isystem"${path.resolve(BASE, 'buildtools', 'third_party', 'libc++', 'trunk', 'include')}"`,
     `-isystem"${path.resolve(BASE, 'buildtools', 'third_party', 'libc++abi', 'trunk', 'include')}"`,
     '-fPIC'