message: add -g flag for release mode
  Including debug information doesn't influence the optimizer.
diff: @@ -133,6 +133,7 @@ FLAGS += '-DUSE_HAL_DRIVER'
  FLAGS += '-mthumb'
  FLAGS += '-mfloat-abi=hard'
  FLAGS += { '-Wall', '-Wdouble-promotion', '-Wfloat-conversion', '-fdata-sections', '-ffunction-sections'}
  +FLAGS += '-g'
  -- linker flags
  LDFLAGS += board.ldflags
  @@ -142,7 +143,7 @@ LDFLAGS += '-Wl,--undefined=uxTopUsedPriority'
  -- debug build
  if tup.getconfig("DEBUG") == "true" then
  - FLAGS += '-g -gdwarf-2'
  + FLAGS += '-gdwarf-2'
  OPT += '-Og'
  else
  OPT += '-O2'
  