Make makefile options settable from envars

Makefile

@@ -4,51 +4,51 @@
 # 1 = enable
 
 # ---- COMPILER/LINKER OPTIONS ----
-ENABLE_CLANG                  := 0
-ENABLE_SWD                    := 0
-ENABLE_OVERLAY                := 0
-ENABLE_LTO                    := 1
+ENABLE_CLANG                  ?= 0
+ENABLE_SWD                    ?= 0
+ENABLE_OVERLAY                ?= 0
+ENABLE_LTO                    ?= 1
 
 # ---- STOCK QUANSHENG FERATURES ----
-ENABLE_UART                   := 1
-ENABLE_AIRCOPY                := 0
-ENABLE_FMRADIO                := 1
-ENABLE_NOAA                   := 0
-ENABLE_VOICE                  := 0
-ENABLE_VOX                    := 1
-ENABLE_ALARM                  := 0
-ENABLE_TX1750                 := 0
-ENABLE_PWRON_PASSWORD         := 0
-ENABLE_DTMF_CALLING           := 1
-ENABLE_FLASHLIGHT             := 1
+ENABLE_UART                   ?= 1
+ENABLE_AIRCOPY                ?= 0
+ENABLE_FMRADIO                ?= 1
+ENABLE_NOAA                   ?= 0
+ENABLE_VOICE                  ?= 0
+ENABLE_VOX                    ?= 1
+ENABLE_ALARM                  ?= 0
+ENABLE_TX1750                 ?= 0
+ENABLE_PWRON_PASSWORD         ?= 0
+ENABLE_DTMF_CALLING           ?= 1
+ENABLE_FLASHLIGHT             ?= 1
 
 # ---- CUSTOM MODS ----
-ENABLE_BIG_FREQ               := 1
-ENABLE_SMALL_BOLD             := 1
-ENABLE_KEEP_MEM_NAME          := 1
-ENABLE_WIDE_RX                := 1
-ENABLE_TX_WHEN_AM             := 0
-ENABLE_F_CAL_MENU             := 0
-ENABLE_CTCSS_TAIL_PHASE_SHIFT := 0
-ENABLE_BOOT_BEEPS             := 0
-ENABLE_SHOW_CHARGE_LEVEL      := 0
-ENABLE_REVERSE_BAT_SYMBOL     := 0
-ENABLE_NO_CODE_SCAN_TIMEOUT   := 1
-ENABLE_AM_FIX                 := 1
-ENABLE_SQUELCH_MORE_SENSITIVE := 1
-ENABLE_FASTER_CHANNEL_SCAN    := 1
-ENABLE_RSSI_BAR               := 1
-ENABLE_AUDIO_BAR              := 1
-ENABLE_COPY_CHAN_TO_VFO       := 1
-ENABLE_SPECTRUM               := 1
-ENABLE_REDUCE_LOW_MID_TX_POWER:= 0
-ENABLE_BYP_RAW_DEMODULATORS   := 0
-ENABLE_BLMIN_TMP_OFF          := 0
-ENABLE_SCAN_RANGES            := 1
+ENABLE_BIG_FREQ               ?= 1
+ENABLE_SMALL_BOLD             ?= 1
+ENABLE_KEEP_MEM_NAME          ?= 1
+ENABLE_WIDE_RX                ?= 1
+ENABLE_TX_WHEN_AM             ?= 0
+ENABLE_F_CAL_MENU             ?= 0
+ENABLE_CTCSS_TAIL_PHASE_SHIFT ?= 0
+ENABLE_BOOT_BEEPS             ?= 0
+ENABLE_SHOW_CHARGE_LEVEL      ?= 0
+ENABLE_REVERSE_BAT_SYMBOL     ?= 0
+ENABLE_NO_CODE_SCAN_TIMEOUT   ?= 1
+ENABLE_AM_FIX                 ?= 1
+ENABLE_SQUELCH_MORE_SENSITIVE ?= 1
+ENABLE_FASTER_CHANNEL_SCAN    ?= 1
+ENABLE_RSSI_BAR               ?= 1
+ENABLE_AUDIO_BAR              ?= 1
+ENABLE_COPY_CHAN_TO_VFO       ?= 1
+ENABLE_SPECTRUM               ?= 1
+ENABLE_REDUCE_LOW_MID_TX_POWER?= 0
+ENABLE_BYP_RAW_DEMODULATORS   ?= 0
+ENABLE_BLMIN_TMP_OFF          ?= 0
+ENABLE_SCAN_RANGES            ?= 1
 
 # ---- DEBUGGING ----
-ENABLE_AM_FIX_SHOW_DATA       := 0
-ENABLE_AGC_SHOW_DATA          := 0
+ENABLE_AM_FIX_SHOW_DATA       ?= 0
+ENABLE_AGC_SHOW_DATA          ?= 0
 
 #############################################################
 
@@ -204,11 +204,11 @@ endif
 OBJCOPY = arm-none-eabi-objcopy
 SIZE = arm-none-eabi-size
 
-AUTHOR_STRING := EGZUMER
+AUTHOR_STRING ?= EGZUMER
 # the user might not have/want git installed
 # can set own version string here (max 7 chars)
 ifneq (, $(shell $(WHERE) git))
-	VERSION_STRING := $(shell git describe --tags --exact-match 2>$(NULL_OUTPUT))
+	VERSION_STRING ?= $(shell git describe --tags --exact-match 2>$(NULL_OUTPUT))
 	ifeq (, $(VERSION_STRING))
     	VERSION_STRING := $(shell git rev-parse --short HEAD)
 	endif