Add flto to packages to be built (#5259)

* Add flto

packages/libgdiplus.rb

@@ -20,7 +20,9 @@ class Libgdiplus < Package
   depends_on 'imake' => :build
 
   def self.build
-    system "./configure #{CREW_OPTIONS} \
+    system  "CFLAGS='-flto=auto' CXXFLAGS='-flto=auto'
+      LDFLAGS='-flto=auto' \
+      ./configure #{CREW_OPTIONS} \
       --with-libexif \
       --with-libtiff \
       --with-jpeg \

packages/libwebp.rb

@@ -17,7 +17,9 @@ class Libwebp < Package
 
   def self.build
     system "env NOCONFIGURE=1 ./autogen.sh"
-    system "./configure #{CREW_OPTIONS} \
+    system  "CFLAGS='-flto=auto' CXXFLAGS='-flto=auto'
+      LDFLAGS='-flto=auto' \
+      ./configure #{CREW_OPTIONS} \
       --enable-libwebpmux \
       --enable-libwebpdemux \
       --enable-libwebpdecoder \