buildroot

gcc: apply patches stored in global patches directories

When building host gcc, patches stored in global patches directories are
skipped. This patch fixes the unexpected behavior.

Signed-off-by: Chunhui He <hchunhui@mail.ustc.edu.cn>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
[Thomas:
 - rename the loop variable from 'D' to 'patchdir'
 - add some additional comments
 - remove final ; at end of loop when applying the patches, since it's
   not needed]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>