scripts: move backtrace marker to CT_WORK_DIR

Avoid error when commands in scripts/crosstool-NG.sh fail
before CT_BUILD_DIR is set.

So we need to remove the backtrace marker of a potential previous
build. Previously, it was implicitly removed because we did remove
the directory it was in, which is no longer the case.

Signed-off-by: Johannes Stezenbach <js@sig21.net>
[yann.morin.1998@free.fr: remove backtrace marker on start of build]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Message-Id: <20121015094615.GA18673@sig21.net>
Patchwork-Id: 191498

Original patch from Gentoo.

-= BEGIN original header =-

-= END original header =-

diff -durN uClibc-0.9.30.orig/Rules.mak uClibc-0.9.30/Rules.mak

--- uClibc-0.9.30.orig/Rules.mak	2008-11-12 13:24:16.000000000 +0100

+++ uClibc-0.9.30/Rules.mak	2009-02-07 09:57:59.000000000 +0100

@@ -519,6 +519,7 @@

 endif

 CFLAGS += $(call check_gcc,-std=gnu99,)

+CFLAGS += $(call check_gcc,-fgnu89-inline,)

 LDFLAGS_NOSTRIP:=$(CPU_LDFLAGS-y) -shared \

 	-Wl,--warn-common -Wl,--warn-once -Wl,-z,combreloc