libvpx excepts gcc to be used as linker. However, it respects
what is defined in LD. The problem is that LD is defined by
OpenWRT as *-ld.

Forcing the LD env for configure and make solves the problem.
Also, the patch that modified ld call to match what *-ld provides
is not needed anymore.

Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>