build: Honour NO_COLOR in include/scan.mk

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Hi all:

This is my first OpenWrt patch. I am a clean, pure newbie! 8-)

Honour NO_COLOR in Makefile function 'progress' in include/scan.mk, in the same way that include/verbose.mk does.

Signed-off-by: R. Diez <rdiezmail-openwrt@yahoo.com>

include/scan.mk

@@ -19,9 +19,15 @@ else
 endif
 
 ifeq ($(IS_TTY),1)
-  define progress
+  ifneq ($(strip $(NO_COLOR)),1)
+    define progress
 	printf "\033[M\r$(1)" >&2;
-  endef
+    endef
+  else
+    define progress
+	:;
+    endef
+  endif
 else
   define progress
 	:;