unbundle: add GN files for ffmpeg, libevent, libxslt, snappy, and yasm

build/linux/unbundle/yasm.gn

+# Copyright 2016 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+if (current_cpu == "x86") {
+  _yasm_flags = [
+    "-felf32",
+    "-m",
+    "x86",
+  ]
+} else if (current_cpu == "x64") {
+  _yasm_flags = [
+    "-DPIC",
+    "-felf64",
+    "-m",
+    "amd64",
+  ]
+}
+
+template("yasm_assemble") {
+  action_name = "${target_name}_action"
+  source_set_name = target_name
+
+  action_foreach(action_name) {
+    # Only the source set can depend on this.
+    visibility = [ ":$source_set_name" ]
+
+    script = "//third_party/yasm/run_yasm.py"
+    sources = invoker.sources
+
+    if (defined(invoker.inputs)) {
+      inputs = invoker.inputs
+    }
+
+    deps = []
+    if (defined(invoker.deps)) {
+      deps += invoker.deps
+    }
+
+    args = [ "yasm" ] + _yasm_flags
+    if (defined(invoker.yasm_flags)) {
+      args += invoker.yasm_flags
+    }
+
+    # User defined include dirs go first.
+    if (defined(invoker.include_dirs)) {
+      foreach(include, invoker.include_dirs) {
+        args += [ "-I" + rebase_path(include, root_build_dir) ]
+      }
+    }
+
+    # Default yasm include dirs. Make it match the native build (source root and
+    # root generated code directory).
+    # This goes to the end of include list.
+    args += [
+      "-I.",
+
+      # Using "//." will produce a relative path "../.." which looks better than
+      # "../../" which will result from using "//" as the base (although both
+      # work). This is because rebase_path will terminate the result in a
+      # slash if the input ends in a slash.
+      "-I" + rebase_path("//.", root_build_dir),
+      "-I" + rebase_path(root_gen_dir, root_build_dir),
+    ]
+
+    # Extra defines.
+    if (defined(invoker.defines)) {
+      foreach(def, invoker.defines) {
+        args += [ "-D$def" ]
+      }
+    }
+
+    # Output file.
+    outputs = [
+      "$target_out_dir/{{source_name_part}}.o",
+    ]
+    args += [
+      "-o",
+      rebase_path(outputs[0], root_build_dir),
+      "{{source}}",
+    ]
+
+    # The wrapper script run_yasm will write the depfile to the same name as
+    # the output but with .d appended (like gcc will).
+    depfile = outputs[0] + ".d"
+  }
+
+  # Gather the .o files into a linkable thing. This doesn't actually link
+  # anything (a source set just compiles files to link later), but will pass
+  # the object files generated by the action up the dependency chain.
+  source_set(source_set_name) {
+    if (defined(invoker.visibility)) {
+      visibility = invoker.visibility
+    }
+
+    sources = get_target_outputs(":$action_name")
+
+    deps = [
+      ":$action_name",
+    ]
+  }
+}