Build with -g by default

Change-Id: I5331319164bb103bc226d4553d883e27411be5a9
diff --git a/pw_build/BUILD.gn b/pw_build/BUILD.gn
index 9383f60..a32e49c 100644
--- a/pw_build/BUILD.gn
+++ b/pw_build/BUILD.gn
@@ -14,6 +14,20 @@
 
 import("$dir_pw_docgen/docs.gni")
 
+# The default config is applied to all targets in Pigweed's BUILDCONFIG.gn.
+config("default") {
+  configs = [
+    ":debugging",
+    ":reduced_size",
+    ":strict_warnings",
+  ]
+}
+
+config("debugging") {
+  # Enable debug symbol generation. This has no effect on final code size.
+  cflags = [ "-g" ]
+}
+
 # Standard compiler flags to reduce output binary size.
 config("reduced_size") {
   cflags = [