gdb: add patches to fix musl build on ppc(64)(le) and sh

gdb: add patches to fix musl build on ppc(64)(le) and sh

This commit small patches to gdb that fix redefined structures build
problems that occur when building on PowerPC, PowerPC64, PowerPC64le and
SuperH with the musl C library.

The PowerPC(64)(le) patch was taken from the Yocto Project, the SuperH
patch was inspired from the PowerPC patch. The issue has also been
reported upstream to the musl developers:

  http://www.openwall.com/lists/musl/2017/06/03/1

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