Bug#1139535: elpa: FTBFS: configure: error: Could not compile an MPI C program

[Graham Inggs]

This may be related to the following change in debhelper 13.32.  See
also #1139889 [1].

 [ Helmut Grohne ]
 * autoconf: export standard build tools


[1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1139889