pw_tool: Create a basic CLI tool framework

Adds a basic framework for a CLI tool for future features. At the time
of this commit, this only includes basic "proof of concept" style
commands, but can and will be extended to more functionality.

Change-Id: I0445384bae7b763d1f1301e427dbb6316faf9ec2
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/29880
Commit-Queue: Jason Graffius <jgraff@google.com>
Reviewed-by: Alexei Frolov <frolv@google.com>
Reviewed-by: Keir Mierle <keir@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index 1d1e617..7cd01b9 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -185,6 +185,12 @@
 
     # Add target-specific images.
     deps += pw_TARGET_APPLICATIONS
+
+    # Add the pw_tool target to be built on host.
+    if (defined(pw_toolchain_SCOPE.is_host_toolchain) &&
+        pw_toolchain_SCOPE.is_host_toolchain) {
+      deps += [ "$dir_pw_tool" ]
+    }
   }
 
   group("host_tools") {
@@ -218,6 +224,7 @@
       "$dir_pw_sync",
       "$dir_pw_sys_io",
       "$dir_pw_thread",
+      "$dir_pw_tool",
       "$dir_pw_trace",
       "$dir_pw_unit_test",
       "$dir_pw_varint",