Link PRIVATE_TARGET_FDO_LIB before shared libraries

For global declaration of FDO profile generation and usage,
we need to link PRIVATE_TARGET_FDO_LIB (libgcov.a by default)
prior to linking shared libraries.

TARGET_FDO_LIB is set if feedback directed optimizations
are in use, so we do not need to worry about consistent size
increases from this change.

Change-Id: I543903f58893816f037c9466f31b19dfe822fdf4