Put PIO "debug" build in the corner (#19975)

buildroot/share/PlatformIO/scripts/common-cxxflags.py

   #"-Wno-maybe-uninitialized",
   #"-Wno-sign-compare"
 ])
+
+# Useful for JTAG debugging
+#
+# It will separe release and debug build folders. 
+# It useful when we need keep two live versions: one debug, for debugging, 
+# other release, for flashing.
+# Without this, PIO will recompile everything twice for any small change.
+# 
+if env.GetBuildType() == "debug":
+	env['BUILD_DIR'] = '$PROJECT_BUILD_DIR/$PIOENV/debug'