scripts: fix sysroot prefix dir

The sysroot prefix dir was broken in #4960f5d9f829 due to a mishap
when making the out-of-sysroot lib/ symlink: the './' was mistakenly
changed into a single '.' .

Although Jonathan suggested restoring the missing '/' to restore it to
normal operation, I prefered using an explicit pushd/popd to be extra
sure of the symlink location and target, along with a fix in the sysroot
relative directory calculation.

Reported-by: Jonathan Grundon <JGrundon@xos.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
(transplanted from e5fc5c9ea78af28d05244ba09cf718cf75470903)

Enable building a pure soft-float compiler without the need for a software

floating point library.

diff -dur gcc-4.0.4.orig/gcc/config.gcc gcc-4.0.4/gcc/config.gcc

--- gcc-4.0.4.orig/gcc/config.gcc	2007-02-02 19:12:28.000000000 +0100

+++ gcc-4.0.4/gcc/config.gcc	2007-02-02 19:12:07.000000000 +0100

@@ -677,7 +677,7 @@

 		tm_defines="TARGET_BIG_ENDIAN_DEFAULT=1 $tm_defines"

 		;;

 	esac

-	tmake_file="${tmake_file} arm/t-arm arm/t-linux"

+	tmake_file="${tmake_file} arm/t-arm arm/t-linux arm/t-arm-elf"

 	extra_parts="crtbegin.o crtbeginS.o crtend.o crtendS.o"

 	gnu_ld=yes

 	;;