pw_build: Switch to pw_* target types

This change replaces the implicit overrides of the default GN target
types in BUILDCONFIG.gn with explicit pw_* versions. This is done to
allow Pigweed to build within larger GN projects without modifying their
BUILDCONFIG files.

Change-Id: I1d1e41d5e9bde8fe076f7031f3c2b98b9630ff70
diff --git a/pw_protobuf_compiler/proto.gni b/pw_protobuf_compiler/proto.gni
index 4a26bdc..92b49d4 100644
--- a/pw_protobuf_compiler/proto.gni
+++ b/pw_protobuf_compiler/proto.gni
@@ -14,6 +14,7 @@
 
 import("$dir_pw_build/input_group.gni")
 import("$dir_pw_build/python_script.gni")
+import("$dir_pw_build/target_types.gni")
 
 # Python script that invokes protoc.
 _gen_script_path =
@@ -72,7 +73,7 @@
   }
 
   # Create a library with the generated source files.
-  source_set(target_name) {
+  pw_source_set(target_name) {
     all_dependent_configs = [ ":$_include_config_target" ]
     deps = [ ":$_gen_target" ]
     public_deps = [ dir_pw_protobuf ] + invoker.gen_deps
@@ -152,7 +153,7 @@
   }
 
   # Create a library with the generated source files.
-  source_set(target_name) {
+  pw_source_set(target_name) {
     all_dependent_configs = [ ":$_include_config_target" ]
     deps = [ ":$_gen_target" ]
     public_deps = [ dir_third_party_nanopb ] + invoker.gen_deps