Revert "Revert "generattor: add --cflags command line flag""

This reverts commit 2ae35c8b46.

generator/generator.sh

@@ -16,10 +16,38 @@
 # arg[2] options as words in one string: internal for imgui_internal generation, freetype for freetype generation, comments for comments generation, nochar to skip char* function version, noimstrv to skip imstrv
 # examples: "" "internal" "internal freetype" "comments internal"
 # arg[3..n] name of implementations to generate and/or CLFLAGS (e.g. -DIMGUI_USER_CONFIG or -DIMGUI_USE_WCHAR32)
+#
+#!/bin/bash
+
+# parse command line arguments
+# ref: https://stackoverflow.com/questions/192249/how-do-i-parse-command-line-arguments-in-bash
+POSITIONAL_ARGS=()
+
+while [[ $# -gt 0 ]]; do
+  case $1 in
+    -c|--cflags)
+      CFLAGS="$2"
+      shift # past argument
+      shift # past value
+      ;;
+    -*|--*)
+      echo "Unknown option $1"
+      exit 1
+      ;;
+    *)
+      POSITIONAL_ARGS+=("$1") # save positional arg
+      shift # past argument
+      ;;
+  esac
+done
+
+set -- "${POSITIONAL_ARGS[@]}" # restore positional parameters
 
 if [[ "$OSTYPE" == "cygwin" || "$OSTYPE" == "msys" || "$OSTYPE" == "win32" ]];
 then
   suffix='.exe'
 fi
 
-luajit$suffix ./generator.lua gcc "internal noimstrv" glfw opengl3 opengl2 sdl2 "$@"
+echo "CFLAGS: " $CFLAGS
+
+luajit$suffix ./generator.lua gcc "internal noimstrv" glfw opengl3 opengl2 sdl2 $CFLAGS