Use -g3 to include macros in debug symbols (#21052)

platformio.ini

   pre:buildroot/share/PlatformIO/scripts/common-dependencies.py
   pre:buildroot/share/PlatformIO/scripts/common-cxxflags.py
   post:buildroot/share/PlatformIO/scripts/common-dependencies-post.py
-build_flags        = -fmax-errors=5 -g -D__MARLIN_FIRMWARE__ -fmerge-constants
+build_flags        = -fmax-errors=5 -g3 -D__MARLIN_FIRMWARE__ -fmerge-constants
 lib_deps           =
 
 #