Change create_symlinks to use gradle-based libraries.

As part of this change, each section clearly identifies
where libraries should be built from. Example from the
source:

LIBS="base:common make:ant-glob ... swt:ddmuilib"
means that:
- "common" is taken from tools/base (gradle)
- "ddmuilib" is taken from tools/swt (gradle)
- "sdkstats" is built using 'make', in which case a
  prebuilt/devtools JAR will be used if it can be found.

Change-Id: Ie793b684f303566a307ee3ff6d6d72db8d26996e