scripts/xldd: better find sysroot with old gcc

Only starting with 4.4 does gcc have a -print-sysroot option.
For 4.3 or before, we have to play some tricks:
- ask gcc where libc.so is,
(we expect it in ${sysroot}/usr/lib/libc.so)
- trim /usr/lib/libc.so from the result

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
(transplanted from aa2305c5b2a57fbcda9a1b5bb5fb3a476ac49a13)

 #!/bin/sh

 SKIP_ME="### CT_NG SKIP ME ###"

 skip_me=$(($(cat "${0}" |@@grep@@ --binary-files=text -o -b -E "^${SKIP_ME}$" |cut -d : -f 1)+${#SKIP_ME}+1))

 dd if="${0}" bs=${skip_me} skip=1 2>/dev/null |bzcat

 exit 0

 ### CT_NG SKIP ME ###