Auto-detect if terminal supports colors

This enables build_oai to detect if the output terminal supports colors.
If it does, it will use colors in its output. If it does not, it will
just print the text, without color codes, improving legibility.

cmake_targets/tools/build_helper

@@ -54,12 +54,17 @@ fi
 ###############################
 ## echo and  family
 ###############################
-red='\E[31m'
-green='\E[32m'
-yellow='\E[33m'
-blue='\E[1;34m'
-reset_color='\E[00m'
-COLORIZE=1
+# only emit color if connected to a terminal, and if it supports colors
+if [ -t 1 ]; then
+  num_colors=$(tput colors)
+  if [ -n "$num_colors" ] && [ "$num_colors" -ge 8 ]; then
+    red='\E[31m'
+    green='\E[32m'
+    yellow='\E[33m'
+    blue='\E[1;34m'
+    reset_color='\E[00m'
+  fi
+fi
 
 cecho()  {
     # Color-echo
@@ -68,8 +73,7 @@ cecho()  {
     local default_msg="No Message."
     message=${1:-$default_msg}
     color=${2:-$green}
-    [ "$COLORIZE" = "1" ] && message="$color$message$reset_color"
-    echo -e "$message"
+    echo -e "$color$message$reset_color"
     return
 }