libc/glibc: fix passing args with spaces when calling backend

Spaces in arguments to the glibc backend were not handled.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

reporter_name="Remy Bohmer"

reporter_url="linux@bohmer.net"

reporter_comment="Example for building a toolchain for m68000 bare metal targets"