"Stephen J. Turnbull" <stephen(a)xemacs.org> writes:
 This is a minor lack of flexibility in M-x build-report.
 build-report looks in several files for a log of your build, then
 cleans out "uninteresting" lines and adds them to report if present.
 If a file is not found, it issues a warning.  It could be made
 possible to silence these warnings via Custom, but it isn't yet. 
You can specify the output file(s) through
M-x customize-variable RET build-report-make-output-files RET
You only have to remember your choice :-)
norbert.