Pins/tests followup (#21268)

Missing commit from #21254
Co-authored-by: Scott Lahteine <github@thinkyhead.com>

buildroot/share/PlatformIO/scripts/common-dependencies-post.py

@@ -0,0 +1,16 @@
+#
+# common-dependencies-post.py
+# Convenience script to add build flags for Marlin Enabled Features
+#
+
+Import("env")
+Import("projenv")
+
+def apply_board_build_flags():
+	if not 'BOARD_CUSTOM_BUILD_FLAGS' in env['MARLIN_FEATURES']:
+		return
+	projenv.Append(CCFLAGS=env['MARLIN_FEATURES']['BOARD_CUSTOM_BUILD_FLAGS'].split())
+
+# We need to add the board build flags in a post script
+# so the platform build script doesn't overwrite the custom CCFLAGS
+apply_board_build_flags()