This is a way do disable DBUG_ENTER()/DBUG_EXIT() stuff which is
needed to dbug trace. Those who doesn't need it may avoid tests
slowdown with -DWITH_DBUG_TRACE=OFF

dbug/tests.c: add define which is neede always in this test

innodb.log_file_name_debug.test: do not depend on DBUG trace stuff
in test

Benchmark results: each test eats less CPU and you can have more
parallel jobs in MTR.

patched:
./mtr -mem -par=8 -suite=innodb  185.34s user 86.85s system 133% cpu 3:23.27 total
./mtr -mem -par=8 -suite=main    80.96s  user 36.01s system 182% cpu 1:04.07 total

main.select                              [ pass ]   1660
main.select                              [ pass ]   1513
main.select                              [ pass ]   1543
main.select                              [ pass ]   1660
main.select                              [ pass ]   1521
main.select                              [ pass ]   1511
main.select                              [ pass ]   1508
main.select                              [ pass ]   1520
main.select                              [ pass ]   1514
main.select                              [ pass ]   1522

vanilla:
./mtr -mem -par=8 -suite=innodb  203.61s user 92.16s system 140% cpu 3:30.16 total
./mtr -mem -par=8 -suite=main    94.11s  user 35.51s system 206% cpu 1:02.69 total

main.select                              [ pass ]   2032
main.select                              [ pass ]   2017
main.select                              [ pass ]   2040
main.select                              [ pass ]   2183
main.select                              [ pass ]   2253
main.select                              [ pass ]   2075
main.select                              [ pass ]   2109
main.select                              [ pass ]   2080
main.select                              [ pass ]   2098
main.select                              [ pass ]   2114