Makefile: check for 'replay' env variable and change build dir accordingly

For replay with the new logger, we want a separate build dir so that the
parameters file and orb rules don't get mixed up.

Makefile

@@ -104,14 +104,21 @@ endif
     PX4_MAKE_ARGS = -j$(j) --no-print-directory
 endif
 
+# check if replay env variable is set & set build dir accordingly
+ifdef replay
+	BUILD_DIR_SUFFIX := _replay
+else
+	BUILD_DIR_SUFFIX :=
+endif
+
 # Functions
 # --------------------------------------------------------------------
 # describe how to build a cmake config
 define cmake-build
-+@if [ $(PX4_CMAKE_GENERATOR) = "Ninja" ] && [ -e $(PWD)/build_$@/Makefile ]; then rm -rf $(PWD)/build_$@; fi
-+@if [ ! -e $(PWD)/build_$@/CMakeCache.txt ]; then Tools/check_submodules.sh && mkdir -p $(PWD)/build_$@ && cd $(PWD)/build_$@ && cmake .. -G$(PX4_CMAKE_GENERATOR) -DCONFIG=$(1) || (cd .. && rm -rf $(PWD)/build_$@); fi
++@if [ $(PX4_CMAKE_GENERATOR) = "Ninja" ] && [ -e $(PWD)/build_$@$(BUILD_DIR_SUFFIX)/Makefile ]; then rm -rf $(PWD)/build_$@$(BUILD_DIR_SUFFIX); fi
++@if [ ! -e $(PWD)/build_$@$(BUILD_DIR_SUFFIX)/CMakeCache.txt ]; then Tools/check_submodules.sh && mkdir -p $(PWD)/build_$@$(BUILD_DIR_SUFFIX) && cd $(PWD)/build_$@$(BUILD_DIR_SUFFIX) && cmake .. -G$(PX4_CMAKE_GENERATOR) -DCONFIG=$(1) || (cd .. && rm -rf $(PWD)/build_$@$(BUILD_DIR_SUFFIX)); fi
 +@Tools/check_submodules.sh
-+@(echo "PX4 CONFIG: $@" && cd $(PWD)/build_$@ && $(PX4_MAKE) $(PX4_MAKE_ARGS) $(ARGS))
++@(echo "PX4 CONFIG: $@$(BUILD_DIR_SUFFIX)" && cd $(PWD)/build_$@$(BUILD_DIR_SUFFIX) && $(PX4_MAKE) $(PX4_MAKE_ARGS) $(ARGS))
 endef
 
 define cmake-build-other