icu4c: fix wildcard

See http://www.cmcrossroads.com/article/trouble-wildcard

$(wildcard) is evaluated at parse-time, not run-time.

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
boost: install DLLs to bin/

Fixes #375.
See   #393.

Signed-off-by: Timothy Gu <timothygu99@gmail.com>