gcc: add patch to support musl on SuperH in gcc 5.x

gcc: add patch to support musl on SuperH in gcc 5.x

Building a toolchain for SuperH/musl works, but the toolchain generate
bogus binaries, because the path to the program interpreter is not
known (and therefore is /dev/null).

This commit backports a patch from gcc 6.x to make SuperH support with
musl work properly.

The patch is not needed in gcc >= 6.x because the musl support is
upstream. The patch is not needed for gcc 4.9 because we had a
different musl support patch that had support for all architectures in
one patch.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
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Changes since v2:
 - None
Changes since v1:
 - New patch in the series