#1384 Reproducibility: Accept NETSNMP_CONFIGURE_OPTIONS from the environment

[Douglas Royds]

To avoid build host paths being written into binaries, accept a null NETSNMP_CONFIGURE_OPTIONS from the environment. NETSNMP_CONFIGURE_OPTIONS can be set either null or to a fixed value. The patch has no effect if NETSNMP_CONFIGURE_OPTIONS is not set.

The change should be Posix compliant. It has been tested on a Linux build only.

[Bart Van Assche]

This patch has been applied on the v5.8 and master branches. Thanks for the patch!