ncurses: Do not pass both -fPIC and -fpic

The configure scripts matches Linux with -fPIC, which is not exactly what
is desired. Since we are already passing $(FPIC), added a CONFIGURE_VAR to
avoid passing -fPIC.

Removed PKG_BUILD_DIR as it is already the default value.

Signed-off-by: Rosen Penev <rosenp@gmail.com>