package/bison: make installation relocatable

Our current host-bison installation is not relocatable, so if you
generate the SDK, and install it in a different location, bison will
no longer work with failures such as:

bison: /home/user/buildroot/output/host/share/bison/m4sugar/m4sugar.m4: cannot open: No such file or directory

This particular issue is already resolved upstream by the addition of
"relocatable" support, which we enable using --enable-relocatable.

Once this issue is fixed, a second one pops up: the path to the m4
program itself is also hardcoded. So we add a patch to fix that as
well. The patch has been submitted upstream, which have requested for
further refinements not applicable to the Buildroot context; in the
meantime, we carry that patch.

Fixes:

  https://bugs.busybox.net/show_bug.cgi?id=12656



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
[yann.morin.1998@free.fr: add reference to the upstream submission]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>