starpufft needs fftwf, not fftwl

examples/Makefile.am

@@ -22,7 +22,7 @@ AM_LDFLAGS = $(STARPU_CUDA_LDFLAGS) $(STARPU_OPENCL_LDFLAGS)
 SUBDIRS = stencil
 
 if STARPU_HAVE_FFTW
-if STARPU_HAVE_FFTWL
+if STARPU_HAVE_FFTWF
 SUBDIRS += starpufft
 endif
 endif