It's not a test as such, since it's got its own main() that takes
arguments, doesn't return a result that can be directly compared
against expected results, and doesn't make use of the test_common
infrastructure.
The CMake build attempts to build all files named test_*.cpp with
test_common, whose main() and load_file() symbols clash with those
that the benchmark provides. Instead of making an exception, let's
rename it to something that doesn't start with "test_". Its usage
message even claims it's called bdecode_benchmark, so we use that.
Also, complete the file listing for test_common in CMake and use
an OBJECT pseudo-library there instead of STATIC. It's just as good
and jives better with having symbols provided by the executable.
(Follow-up patch in the works to provide Asio symbols that way.)
test_natpmp is a proper test but doesn't currently build,
so exclude it from the build for now.
arvidn