smr_with_build_path

This macro adds a "--with-build-path" option to the configure script. This configure option provides a convenient way to add "-I" options to CPPFLAGS and "-L" options to LDFLAGS, at configure time.

Invoking "./configure --with-build-path=DIR" results in "-I DIR/include" being added to CPPFLAGS if DIR/include exists, and "-L DIR/lib" being added to LDFLAGS if DIR/lib exists.

Separate multiple directories using colons; e.g. "--with-build-path=DIR1:DIR2:DIR3".