Remove literal quotes when Perl-script is calling `bench'.

Currently, the `bench.exe' program is failing with an `assert' (out of format) error.  So "make check" fails:

------------------------------Output start------------------------------------------
Making check in tests
make[1]: Entering directory `/d/Dev-Cpp/zztmp/_math/FFTW/fftw-3.3.3/tests'
make  check-local
make[2]: Entering directory `/d/Dev-Cpp/zztmp/_math/FFTW/fftw-3.3.3/tests'
perl -w ./check.pl  -r -c=30 -v `pwd`/bench.exe
Executing "d:/Dev-Cpp/zztmp/_math/FFTW/fftw-3.3.3/tests/bench.exe --verbose=1   --verify 'okd9e11x5e00v24' --verify 'ikd9e11x5e00v24' [..]"
bench: problem.c:96: assertion failed: isdigit(*s)
FAILED d:/Dev-Cpp/zztmp/_math/FFTW/fftw-3.3.3/tests/bench.exe:  --verify 'okd9e11x5e00v24' --verify 'ikd9e11x5e00v24' [..]
Makefile:598: recipe for target `check-local' failed
[..]
make: *** [check-recursive] Error 1
----------------------------------Output end--------------------------------------