debug/ltrace: fix LDFLAGS for libsupc++ and libiberty

The configure script correctly detects libsupc++ and libiberty, but in
the linker stage it tries to link in both libraries without taking care
of the test result.

Signed-off-by: Robert Schwebel <r.schwebel@pengutronix.de>
[yann.morin.1998@anciens.enib.fr: rework patch depth to be -p1]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

reporter_name="Yann E. MORIN"

reporter_url="http://ymorin.is-a-geek.org/projects/crosstool"

reporter_comment="Experimental toolchain for ARM cortex-m3 in Thumb-only, noMMU, and newlib."