grub2: fix do_configure failure when largefile is not in DISTRO_FEATURES

grub2: fix do_configure failure when largefile is not in DISTRO_FEATURES

When 'largefile' is not in DISTRO_FEATURES, '--disable-largefile' is passed
to the configure options. However, the configure script checks the size
of off_t regardless of this option. This raises the following error.

  configure: error: Large file support is required

This patch fixes the above problem.

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>