Config changes to support target_os="fuchsia"

build/config/fuchsia/BUILD.gn

+# Copyright 2017 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.
+
+import("//build/config/sysroot.gni")
+
+assert(is_fuchsia)
+assert(is_posix)
+
+config("compiler") {
+  configs = [
+    ":compiler_sysroot",
+    ":compiler_target",
+  ]
+
+  libs = [
+    "mxio",
+    "magenta",
+    "unwind",
+  ]
+}
+
+config("compiler_sysroot") {
+  # The sole purpose of SYSROOT_VERSION is to change the command line on every
+  # sysroot update so as to force rebuilds.
+  defines = [ "SYSROOT_VERSION=$sysroot_version" ]
+  cflags = [ "--sysroot=" + rebase_path(sysroot, root_build_dir) ]

[Nico, 2017/05/11 18:04:14]

https://cs.chromium.org/chromium/src/build/config/posix/BUILD.gn?type=cs&q=%5...
doesn't work for you for some reason, yes?

[scottmg, 2017/05/11 18:16:36]

Huh, I thought it didn't (I have no idea why I would have added !is_fuchsia
there otherwise) but I just tried it now and it seems fine.

+  ldflags = [ "--sysroot=" + rebase_path(sysroot, root_build_dir) ]
+  asmflags = cflags
+}
+
+config("compiler_target") {
+  cflags = []
+  ldflags = []
+  if (current_cpu == "arm64") {
+    cflags += [ "--target=aarch64-fuchsia" ]
+    ldflags += [ "--target=aarch64-fuchsia" ]
+  } else if (current_cpu == "x64") {
+    cflags += [ "--target=x86_64-fuchsia" ]
+    ldflags += [ "--target=x86_64-fuchsia" ]
+  } else {
+    assert(false, "Unsupported architecture")
+  }
+  asmflags = cflags
+}