Add option to build libbluetooth as staticlib

For ChromeOS/Linux, we want to build a static libbluetooth to make it
easier to find build breakages earlier and to simplify some of the build
issues. This change adds a compile time define to choose between using
dlsym to load libbluetooth and using extern to access the symbols
directly.

Bug: 176847256
Tag: #floss
Test: atest --host bluetooth_test_gd
Change-Id: I818c0f4a7baf414e73dc6f6ae73bb3e3bc3f357f