configure: add cflags in uriparser check when --prefix set
configure: add cflags in uriparser check when --prefix set

For example, when cross-compiling using mingw the AC_CHECK_LIB
test for uriparser compiled a program that didn't have the
--prefix path set in the configure command. The program failed
to link. The solution is to include {prefix}/include and
{prefix}/lib in the CFLAGS.

ebu/ebu-bmx,xunchangguo/BMX,kierank/bmxlib-bmx,kierank/bmxlib-bmx,ebu/ebu-bmx,Limecraft/ebu-bmx,stuarthicks/bmx,Limecraft/ebu-bmx,xunchangguo/BMX,xunchangguo/BMX,Limecraft/ebu-bmx,kierank/bmxlib-bmx,stuarthicks/bmx,ebu/ebu-bmx,stuarthicks/bmx