Trial auto-detection of libraries

binding.gyp

@@ -1,9 +1,9 @@
 {
   'variables': {
     'GTK_Root%': 'C:/GTK',  # Set the location of GTK all-in-one bundle
-    'with_jpeg%': 'false',
-    'with_gif%': 'false',
-    'with_pango%': 'false'
+    'with_jpeg%': '<!(./has_lib.sh jpeg)',
+    'with_gif%': '<!(./has_lib.sh gif)',
+    'with_pango%': '<!(./has_lib.sh pangocairo)'
   },
   'targets': [
     {

has_lib.sh

@@ -0,0 +1,23 @@
+#!/usr/bin/env bash
+has_lib() {
+  local lib=$1
+
+  # Try using ldconfig on linux systems
+  for LINE in `which ldconfig > /dev/null && ldconfig -p 2>/dev/null | grep lib$lib`; do
+    return 0
+  done
+
+  # Try just checking common library locations
+  for dir in /lib /usr/lib /usr/local/lib /opt/local/lib; do
+    test -d $dir && ls $dir | grep $lib && return 0
+  done
+
+  return 1
+}
+
+has_lib $1 > /dev/null
+if test $? -eq 0; then
+  echo true
+else
+  echo false
+fi