feat: CLI-only version (without GTK)

Modify the build system and the source
files to support building a CLI-only
version with only glib2 as a dependency.
Use CLI_ONLY=1 ./configure, then make clean all.

scripts/bash-based-configure

@@ -1364,6 +1364,7 @@ EOF
 
    cat >conftest.c <<EOF
 #include <glib.h>
+#include <stdio.h>
 int main(int argc, char *argv[])
 { g_malloc(1024);