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_build/linker_script.gni b/pw_build/linker_script.gni
index 7c5abf2..4b208bf 100644
--- a/pw_build/linker_script.gni
+++ b/pw_build/linker_script.gni
@@ -13,6 +13,7 @@
 # the License.
 
 import("$dir_pw_build/exec.gni")
+import("$dir_pw_build/target_types.gni")
 
 # Preprocess a linker script and turn it into a target.
 #
@@ -111,7 +112,7 @@
 
   # The target that adds the linker script config to this library and everything
   # that depends on it.
-  source_set(target_name) {
+  pw_source_set(target_name) {
     inputs = [ _final_linker_script ]
     if (defined(invoker.inputs)) {
       inputs += invoker.inputs