[build] more portable autogen.sh shell script
[build] more portable autogen.sh shell script

Use more portable shell function definition, better supported by /bin/sh

Some /bin/sh, e.g. dash, do not support trap on ERR,
so that will issue some trace and will not trigger on ERR,
but the rest of the script runs fine.

gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4