Config changes to support target_os="fuchsia"

build/config/fuchsia/BUILD.gn

Index: build/config/fuchsia/BUILD.gn
diff --git a/build/config/fuchsia/BUILD.gn b/build/config/fuchsia/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..9ec7b11ddc5a2eff38f48ce87aa5c2d6fa7d3411
--- /dev/null
+++ b/build/config/fuchsia/BUILD.gn
@@ -0,0 +1,30 @@
+# 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") {
+  defines = [ "SYSROOT_VERSION=$sysroot_version" ]
+  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
+
+  libs = [
+    "mxio",
+    "magenta",
+    "unwind",
+  ]
+}