gnu-config: use /usr/bin/env perl instead of /usr/bin/perl in gnu-configize.in

gnu-config: use /usr/bin/env perl instead of /usr/bin/perl in gnu-configize.in

* fixes errors like this
  | /OE/tmpdir-shr/sysroots/armv4t-oe-linux-gnueabi/usr/share/aclocal/libpcap.m4:40: warning: underquoted definition of AC_LBL_C_INIT_BEFORE_CC
  | /OE/tmpdir-shr/sysroots/armv4t-oe-linux-gnueabi/usr/share/aclocal/libpcap.m4:40:   run info '(automake)Extending aclocal'
  | /OE/tmpdir-shr/sysroots/armv4t-oe-linux-gnueabi/usr/share/aclocal/libpcap.m4:40:   or see http://sources.redhat.com/automake/automake.html#Extending-aclocal
  | autoreconf: running: /OE/tmpdir-shr/sysroots/x86_64-linux/usr/bin/autoconf --include=/OE/tmpdir-shr/work/armv4t-oe-linux-gnueabi/efreet-2_1.0.999+svnr56704-r0.0/efreet/m4/ --include=/OE/tmpdir-shr/sysroots/armv4t-oe-linux-gnueabi/usr/share/aclocal-1.11 --include=/OE/tmpdir-shr/sysroots/armv4t-oe-linux-gnueabi/usr/share/aclocal --force --warnings=cross
  | autoreconf: running: /OE/tmpdir-shr/sysroots/x86_64-linux/usr/bin/autoheader --include=/OE/tmpdir-shr/work/armv4t-oe-linux-gnueabi/efreet-2_1.0.999+svnr56704-r0.0/efreet/m4/ --include=/OE/tmpdir-shr/sysroots/armv4t-oe-linux-gnueabi/usr/share/aclocal-1.11 --include=/OE/tmpdir-shr/sysroots/armv4t-oe-linux-gnueabi/usr/share/aclocal --force --warnings=cross
  | autoreconf: running: automake --foreign --add-missing --copy --force-missing --warnings=cross
  | automake: unknown warning category cross
  | autoreconf: running: gnu-configize
  | /usr/bin/perl: symbol lookup error: /OE/tmpdir-shr/sysroots/x86_64-linux/usr/lib/perl/5.10.1/auto/IO/IO.so: undefined symbol: Perl_Istack_sp_ptr
  | autoreconf: gnu-configize failed with exit status: 127

* or like this:
  | Perl lib version (5.10.1) doesn't match executable version (v5.12.3) at /OE/tmpdir-shr/sysroots/x86_64-linux/usr/lib/perl/5.10.1/Config.pm line 50."

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>