Ensure compatibility with a single shared libvips library

See: libvips#372.

lib/vips.rb

@@ -25,11 +25,28 @@
 #   "lib" prefix or a ".dll" suffix.
 def library_name(name, abi_number)
   if FFI::Platform.windows?
-    "lib#{name}-#{abi_number}.dll"
+    # On Windows, `GetProcAddress()` can only search in a specified DLL and
+    # doesn't look into its dependent libraries for symbols. Therefore, we
+    # check if the GLib DLLs are available. If these can not be found, we
+    # assume that GLib is statically linked into libvips.
+    begin
+      lib = FFI::DynamicLibrary.open("lib#{name}-#{abi_number}.dll", 
+        FFI::DynamicLibrary::RTLD_LAZY | FFI::DynamicLibrary::RTLD_LOCAL)
+      return lib if lib
+
+    # LoadError for JRuby, RuntimeError for TruffleRuby
+    rescue LoadError, RuntimeError
+      return "libvips-42.dll"
+    end
+
+  # macOS and *nix uses `dlsym()`, which also searches for named symbols
+  # in the dependencies of the shared library. Therefore, we can support
+  # a single shared libvips library with all dependencies statically
+  # linked.
   elsif FFI::Platform.mac?
-    "#{name}.#{abi_number}"
+    "vips.42"
   else
-    "#{name}.so.#{abi_number}"
+    "vips.so.42"
   end
 end