Remove '-std=c99' from ICU_CFLAGS. We want '-std=c11'. Why, oh why must
icu-config supply flags which have nothing to do with using ICU?
Temporarily (?) switched to ICU 51 because we can't get 32-bit mingw
builds to link statically with ICU 50. This creates some kind of symbol
conflict with boost::thread. Teh intarwebs say it can be "resolved"
by adding '-Wl,--allow-multiple-definition' to LDFLAGS. Go read the
description of --allow-multiple-definition in the man page for ld. It's
frankly one of the scarriest flag descriptions I've ever seen. This is
just asking for a world of pain.