build: add -Wno-attributes for PX4

This will allow us to use [[fallthrough]] attribute as an
statement.

Tools/ardupilotwaf/boards.py

@@ -495,6 +495,7 @@ class px4(Board):
             '-Wlogical-op',
             '-Wframe-larger-than=1300',
             '-fsingle-precision-constant',
+            '-Wno-attributes',
             '-Wno-error=double-promotion',
             '-Wno-error=missing-declarations',
             '-Wno-error=float-equal',

mk/px4_targets.mk

@@ -51,7 +51,7 @@ PX4_V4PRO_CONFIG_FILE=$(MK_DIR)/PX4/config_px4fmu-v4pro_APM.mk
 # because this platform lacks most of the standard library and STL. Hence we need to force C++03 mode.
 SKETCHFLAGS=$(SKETCHLIBINCLUDES) -DUAVCAN_CPP_VERSION=UAVCAN_CPP03 -DUAVCAN_NO_ASSERTIONS -DUAVCAN_NULLPTR=nullptr -DARDUPILOT_BUILD -DTESTS_MATHLIB_DISABLE -DCONFIG_HAL_BOARD=HAL_BOARD_PX4 -DSKETCHNAME="\\\"$(SKETCH)\\\"" -DSKETCH_MAIN=ArduPilot_main -DAPM_BUILD_DIRECTORY=APM_BUILD_$(SKETCH)
 
-WARNFLAGS = -Wall -Wextra -Wlogical-op -Werror -Wno-unknown-pragmas -Wno-redundant-decls -Wno-psabi -Wno-packed -Wno-error=double-promotion -Wno-error=unused-variable -Wno-error=reorder -Wno-error=float-equal -Wno-error=pmf-conversions -Wno-error=missing-declarations -Wno-error=unused-function
+WARNFLAGS = -Wall -Wextra -Wlogical-op -Werror -Wno-attributes -Wno-unknown-pragmas -Wno-redundant-decls -Wno-psabi -Wno-packed -Wno-error=double-promotion -Wno-error=unused-variable -Wno-error=reorder -Wno-error=float-equal -Wno-error=pmf-conversions -Wno-error=missing-declarations -Wno-error=unused-function
 OPTFLAGS = -fsingle-precision-constant
 
 # avoid PX4 submodules