pw_assert: Initial assert module

This starts the assert and assert_basic modules, which are the beginning
of our assert foundation. Much more is needed; in particular the "tests"
don't really do much other than check for compilation.

Screenshot
==========

   ▄████▄      ██▀███      ▄▄▄           ██████     ██░ ██
  ▒██▀ ▀█     ▓██ ▒ ██▒   ▒████▄       ▒██    ▒    ▓██░ ██▒
  ▒▓█ 💥 ▄    ▓██ ░▄█ ▒   ▒██  ▀█▄     ░ ▓██▄      ▒██▀▀██░
  ▒▓▓▄ ▄██▒   ▒██▀▀█▄     ░██▄▄▄▄██      ▒   ██▒   ░▓█ ░██
  ▒ ▓███▀ ░   ░██▓ ▒██▒    ▓█   ▓██▒   ▒██████▒▒   ░▓█▒░██▓
  ░ ░▒ ▒  ░   ░ ▒▓ ░▒▓░    ▒▒   ▓▒█░   ▒ ▒▓▒ ▒ ░    ▒ ░░▒░▒
    ░  ▒        ░▒ ░ ▒░     ▒   ▒▒ ░   ░ ░▒  ░ ░    ▒ ░▒░ ░
  ░             ░░   ░      ░   ▒      ░  ░  ░      ░  ░░ ░
  ░ ░            ░              ░  ░         ░      ░  ░  ░
  ░

  Welp, that didn't go as planned. It seems we crashed. Terribly sorry!

  CRASH MESSAGE

     Check failed: x (=50) > y (=51300): You SHOULD see this message

  CRASH FILE & LINE

     ../../pw_assert/assert_test.cc:46

  CRASH FUNCTION

     PigweedTestBody

==========

Change-Id: I9dbb460b3b33040d8009749f44b9fc174e2c8138

1 files changed, 51 insertions, 0 deletions

diff --git a/pw_assert_basic/BUILD.gn b/pw_assert_basic/BUILD.gn
new file mode 100644
index 000000000..f9f77e0cf
--- /dev/null
+++ b/pw_assert_basic/BUILD.gn
@@ -0,0 +1,51 @@
+# Copyright 2020 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("default_config") {
+  include_dirs = [ "public" ]
+}
+
+config("backend_config") {
+  include_dirs = [ "public_overrides" ]
+}
+
+if (dir_pw_assert_backend == dir_pw_assert_basic) {
+  source_set("pw_assert_basic") {
+    public_configs = [
+      ":backend_config",
+      ":default_config",
+    ]
+    deps = [
+      ":core",
+    ]
+    public = [
+      "public_overrides/pw_assert_backend/assert_backend.h",
+    ]
+    sources = public
+  }
+}
+
+source_set("core") {
+  public_configs = [ ":default_config" ]
+  deps = [
+    "$dir_pw_assert:facade",
+    "$dir_pw_dumb_io",
+    "$dir_pw_preprocessor",
+    "$dir_pw_string",
+  ]
+  public = [
+    "public/pw_assert_basic/assert_basic.h",
+  ]
+  sources = public + [ "assert_basic.cc" ]
+}