[perf] make clean problematic bashism

["Wouter M. Koolen" <W.M.Koolen-Wijkstra@cwi.nl>]

Dear perf maintainers,

I attempted to compile perf 3.5.1 without worrying about installing 
dependencies first. The resulting error messages were quite helpful, and 
led me to install a bunch of development libraries and flex.

Unfortunately, after installing flex the build still failed, even after 
make clean.

The reason for this was a bunch of generated empty flex files in util/ 
that were not removed by make clean. They are intended to be erased, 
since the Makefile executes

rm -f util/*-{bison,flex}*

however, this command does not remove the files. I guess because {,} 
alternatives are only special in bash but the makefile is run with some 
other shell?

I got perf to compile now, but thought you would be interested to know 
about this little problem.

With kind regards,

Wouter Koolen


PS: as a side note: GNU make has the .DELETE_ON_ERROR: special target, 
which removes the target file when its generating command fails. This 
would have prevented my problem and sounds like a good idea in general. 
Maybe perf could make use of this feature when on GNU make?