Add an option --enable-shrink-binary-size to configure.

This option could reduce the LLVM tools by "-fdata-sections, -ffunction-sections"
and "--gc-sections". Note that with --enable-shrink-binary-size, your LLVM tools
might not be able to load plugins (ex: LLVMPolly).

The default is off to make NDK llvm tools support plugin.

Change-Id: Ia9aee193a82132da632b706827e7ec7d427014a7