tests: clean up built binaries after running test-fuzz-targets.t

Most users won't notice a change here because they won't have the
fuzzer infra, but by good fortune my workstation has the required bits
and keeps leaving the fuzzer binaries around.

Differential Revision: https://phab.mercurial-scm.org/D6862

tests/test-fuzz-targets.t

@@ -1,43 +1,46
 #require test-repo
 
   $ cd $TESTDIR/../contrib/fuzz
 
 which(1) could exit nonzero, but that's fine because we'll still end
 up without a valid executable, so we don't need to check $? here.
 
   $ if which gmake >/dev/null 2>&1; then
   >     MAKE=gmake
   > else
   >     MAKE=make
   > fi
 
   $ havefuzz() {
   >     cat > $TESTTMP/dummy.cc <<EOF
   > #include <stdlib.h>
   > #include <stdint.h>
   > int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) { return 0; }
   > int main(int argc, char **argv) {
   >     const char data[] = "asdf";
   >     return LLVMFuzzerTestOneInput((const uint8_t *)data, 4);
   > }
   > EOF
   >     $CXX $TESTTMP/dummy.cc -o $TESTTMP/dummy \
   >        -fsanitize=fuzzer-no-link,address || return 1
   > }
 
 #if clang-libfuzzer
   $ CXX=clang++ havefuzz || exit 80
   $ $MAKE -s clean all
 #endif
 #if no-clang-libfuzzer clang-6.0
   $ CXX=clang++-6.0 havefuzz || exit 80
   $ $MAKE -s clean all CC=clang-6.0 CXX=clang++-6.0
 #endif
 #if no-clang-libfuzzer no-clang-6.0
   $ exit 80
 #endif
 
 Just run the fuzzers for five seconds each to verify it works at all.
   $ ./bdiff -max_total_time 5
   $ ./mpatch -max_total_time 5
   $ ./xdiff -max_total_time 5
+
+Clean up.
+  $ $MAKE -s clean