Build fails under OpenBSD amd64/7.5-stable due to missing math library

[morgant]

When attempting to build under OpenBSD amd64/7.5-stable using Makefile.bsd-wrapper linking fails due to missing math (m) library:

$ make -f Makefile.bsd-wrapper
cc -O2 -pipe -Wall -I/usr/local/include -I/usr/X11R6/include  -MD -MP  -c spectrogram.c
cc -O2 -pipe -Wall -I/usr/local/include -I/usr/X11R6/include  -MD -MP  -c fft.c
cc -O2 -pipe -Wall -I/usr/local/include -I/usr/X11R6/include  -MD -MP  -c cms.c
cc -O2 -pipe -Wall -I/usr/local/include -I/usr/X11R6/include  -MD -MP  -c aux.c
cc -O2 -pipe -Wall -I/usr/local/include -I/usr/X11R6/include  -MD -MP  -c widget.c
cc -O2 -pipe -Wall -I/usr/local/include -I/usr/X11R6/include  -MD -MP  -c sio.c
cc -Wall  -o spectrogram spectrogram.o fft.o cms.o aux.o widget.o sio.o -L/usr/local/lib -L/usr/X11R6/lib -lfftw3 -lX11 -lsndio
ld: error: undefined symbol: cos
>>> referenced by fft.c
>>>               fft.o:(init_fft)

ld: error: undefined symbol: cabs
>>> referenced by fft.c
>>>               fft.o:(exec_fft)
>>> did you mean: fabs
>>> defined in: /usr/lib/libc.so.99.0
cc: error: linker command failed with exit code 1 (use -v to see invocation)
*** Error 1 in /home/linetrace/Projects/spectrogram (<bsd.prog.mk>:126 'spectrogram')

[morgant]

I've submitted PR #4 which resolves this and updates the README with instructions for using the Makefile.bsd-wrapper under OpenBSD.

[dim13]

Resolved with #4