mwaw: fix build failure with clang (work around libtool stupidity)

Clang warns about unused -I parameters, and the libtool configure check
for lt_cv_prog_compiler_pic_works_CXX mis-interprets that and declares
-fPIC is not supported.

Change-Id: I0802719142c5a96bc672be299d6e94a1b2d27001
external: fortunately boost no longer requires config_host.mk

Change-Id: I8f2176500bf620cd5e4cdf434e6122b6163b3e0f