Add stm32f429i-disc1 target and pw_dumb_io

Adds both the stm32f429i-disc1 target and a pw_dumb_io uart-based
backend.

Change-Id: If24379118fc2877485653d61ca66ceeb59ef920a
diff --git a/pw_dumb_io_baremetal_stm32f429/BUILD.gn b/pw_dumb_io_baremetal_stm32f429/BUILD.gn
new file mode 100644
index 0000000..d467a41
--- /dev/null
+++ b/pw_dumb_io_baremetal_stm32f429/BUILD.gn
@@ -0,0 +1,40 @@
+# Copyright 2019 The Pigweed Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may not
+# use this file except in compliance with the License. You may obtain a copy
+# of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+config("linker_script_config") {
+  _linker_script = "stm32f429.ld"
+  inputs = [
+    _linker_script,
+  ]
+  ldflags = [ "-T" + rebase_path("$_linker_script") ]
+}
+
+source_set("linker_script") {
+  public_configs = [ ":linker_script_config" ]
+}
+
+source_set("pw_dumb_io_baremetal_stm32f429") {
+  public_configs = [ "$dir_pw_build:pw_default_cpp" ]
+  public_deps = [
+    ":linker_script",
+  ]
+  deps = [
+    "$dir_pw_dumb_io:facade",
+    "$dir_pw_preprocessor",
+  ]
+  sources = [
+    "core_init.c",
+    "dumb_io_baremetal.cc",
+  ]
+}