package/gdb: fix compilation for arc-2018.09 in some cases

package/gdb: fix compilation for arc-2018.09 in some cases

In some cases which seem to depend on how toolchain headers
got installed or configured we may face well-known by now failure
fixed in upstream with [1]:
------------------------------>8----------------------------
In file included from nat/linux-ptrace.c:20:
nat/linux-ptrace.h:175:22: error: expected identifier before numeric constant
 # define TRAP_HWBKPT 4
                      ^
nat/linux-ptrace.h:175:22: error: expected '}' before numeric constant
In file included from .../output/host/arc-buildroot-linux-gnu/sysroot/usr/include/signal.h:58,
                 from build-gnulib/import/signal.h:52,
                 from .../output/host/arc-buildroot-linux-gnu/sysroot/usr/include/sys/wait.h:36,
                 from ./common/gdb_wait.h:23,
                 from nat/linux-ptrace.c:24:
.../output/host/arc-buildroot-linux-gnu/sysroot/usr/include/bits/siginfo-consts.h:156:1: note: to match this '{'
 {
 ^
In file included from nat/linux-ptrace.c:20:
nat/linux-ptrace.h:175:22: error: expected unqualified-id before numeric constant
 # define TRAP_HWBKPT 4
                      ^
In file included from .../output/host/arc-buildroot-linux-gnu/sysroot/usr/include/features.h:428,
                 from .../output/host/arc-buildroot-linux-gnu/sysroot/usr/include/bits/libc-header-start.h:33,
                 from .../output/host/arc-buildroot-linux-gnu/sysroot/usr/include/stdio.h:27,
                 from build-gnulib/import/stdio.h:43,
                 from ./common/common-defs.h:52,
                 from nat/linux-ptrace.c:19:
.../output/host/arc-buildroot-linux-gnu/sysroot/usr/include/sys/wait.h:158:1: error: expected declaration before '}' token
 __END_DECLS
 ^~~~~~~~~~~
------------------------------>8----------------------------

Back-porting the fix for ARC now to get predictably successful results.

[1] https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=5a6c3296a7a90694ad4042f6256f3da6d4fa4ee8

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>