package/gdb: add support for gdb 8.0

package/gdb: add support for gdb 8.0

Add a dependency on gcc >= 4.8 since gdb needs a C++11 compiler.

Remove included patch since 7.12.1:
0001-Remove-const-in-xtensa-linux-nat.c-fetch_gregs.patch
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=d274ecf4ddf76768af57e27f654b9ce6784b391c

Rebase remaining patches:
0002-ppc-ptrace-Define-pt_regs-uapi_pt_regs-on-GLIBC-syst.patch
0003-sh-ptrace-Define-pt_-dsp-regs-uapi_pt_-dsp-regs-on-G.patch

See https://sourceware.org/ml/gdb-announce/2017/msg00003.html

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>