The rework of the host tools discovery caused automake to embed
absolute paths to staging_dir/host/bin/perl into the shebang
of the generated automake executables.

Switch to the portable "/usr/bin/env perl" and enable global
warnings through "$^W" instead of the "-w" interpreter argument.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@44972 3c298f89-4303-0410-b956-a3cf2f4a3e73