Always raise proguard libraries

The platform build system doesn't have the concept of a "compile sdk
version", it uses the "min sdk version" throughout the compilation
process.  This means that no stage of the compilation process can
introduce references to APIs that do not exist in the selected
LOCAL_MIN_SDK_VERSION without causing problems.  Support library
worked around this by effectively making the "compile sdk version"
"current" when running proguard if support library was in the direct
dependency list.

Extend the support library hack everywhere, and always use "current"
or the full bootclasspath when running proguard.

Test: m checkbuild
Change-Id: Iaf5853361767f0ea3e9ad4ec908aadd72d639c79