build: [gn] use platform-appropriate shlib_suffix when building node

build/node/BUILD.gn

@@ -48,6 +48,19 @@ action("gyp_node") {
     "$target_out_dir/$node_configuration/build.ninja",
   ]
 
+  # By default, node will build a dylib called something like
+  # libnode.$node_module_version.dylib, which is inconvenient for our
+  # purposes (since it makes the library's name unpredictable). This forces
+  # it to drop the module_version from the filename and just produce
+  # `libnode.dylib`.
+  if (is_mac) {
+    shlib_suffix = "dylib"
+  } else if (is_win) {
+    shlib_suffix = "dll"
+  } else if (is_linux) {
+    shlib_suffix = "so"
+  }
+
   args = [
     "-I", rebase_path("$target_gen_dir/config.gypi", root_build_dir),
     "-I", rebase_path("node_override.gypi", root_build_dir),
@@ -56,6 +69,9 @@ action("gyp_node") {
     "-D", "target_arch=$target_cpu",
     "-D", "host_arch=$host_cpu",
     "-D", "config_gypi=" + rebase_path("$target_gen_dir/config.gypi"),
+    # This has _gn suffixed otherwise it gets overridden by a shlib_suffix
+    # that's set in node's gyp files. Don't ask me 🤷
+    "-D", "shlib_suffix_gn=" + shlib_suffix,
     "-Goutput_dir=./$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

@@ -4,12 +4,7 @@
     # that we're building v8 with icu, so force it on.
     'v8_enable_inspector': 1,
 
-    # By default, node will build a dylib called something like
-    # libnode.$node_module_version.dylib, which is inconvenient for our
-    # purposes (since it makes the library's name unpredictable). This forces
-    # it to drop the module_version from the filename and just produce
-    # `libnode.dylib`.
-    'shlib_suffix': 'dylib',
+    'shlib_suffix': '<(shlib_suffix_gn)',
   },
   'target_defaults': {
     'target_conditions': [