Simplify the color filter

The color filter is now entirely based on the "true &&" prefix for build steps.

Signed-off-by: Christophe de Dinechin <christophe@dinechin.org>

config.mk

@@ -219,9 +219,7 @@ SEDOPT_windows=	-u
 
 # Colorize warnings, errors and progress information
 LINE_BUFFERED=--line-buffered
-COLOR_FILTER=   | grep $(LINE_BUFFERED) -v -e "^true &&" -e "^[A-Za-z0-9_-]\+\.\(c\|h\|cpp\|hpp\)$$"            \
-	    $(COLORIZE)
-
+COLOR_FILTER=   | grep $(LINE_BUFFERED) -v -e "^true &&" $(COLORIZE)
 COLORIZE= | sed $(SEDOPT_$(OS_NAME))                                                                        		\
             -e 's/^\(.*[,:(]\{1,\}[0-9]*[ :)]*\)\([Ww]arning\)/$(POS_COLOR)\1$(WRN_COLOR)\2$(DEF_COLOR)/g'  		\
             -e 's/^\(.*[,:(]\{1,\}[0-9]*[ :)]*\)\([Ee]rror\)/$(POS_COLOR)\1$(ERR_COLOR)\2$(DEF_COLOR)/g'    		\