fix handling of absolute build paths

When building under the BDK, some paths are absolute instead of relative,
so we end up appending an absolute path to an absolute path which breaks.
Add explicit checks to each possible absolute path before we try to make
it into one by hand.

TEST=`m -j32` w/libpng under bdk works
TEST=`lunch && make` w/python works
TEST=`make PRODUCT-brilloemulator_arm-eng` w/python works

Change-Id: I89070760bc849ac652c2e4a71055d66da763792c
2 files changed