debug/gdb: fix runtime sysroot

This patch sets the runtime sysroot to fix the following GDB warning:
"Unable to find dynamic linker breakpoint function.
GDB will be unable to debug shared library initializers
and track explicitly loaded dynamic code."

The sysroot can later be changed within gdb with the `set sysroot`
command if necessary.

Signed-off-by: "Benoît THÉBAUDEAU" <benoit.thebaudeau@advansee.com>

syntax: glob

# Generated files

Makefile

ct-ng

docs/ct-ng.1

docs/ct-ng.1.gz

paths.mk

scripts/crosstool-NG.sh

scripts/saveSample.sh

scripts/showTuple.sh

kconfig/conf

kconfig/?conf

kconfig/**.o

kconfig/**.dep

config.gen/

.config

.config.2

# Temporaries

.*.swp

build.log

.config.old

# This is the place where toolchains are built

.build/

# .. and the legacy location

targets/