Add --disable-starpufft configuration option

configure.ac

@@ -1337,6 +1337,10 @@ have_fftwf=no
 have_fftwl=no
 fft_support=no
 
+AC_ARG_ENABLE(starpufft, [AS_HELP_STRING([--disable-starpufft],
+			[Disable build of StarPU-FFT])],
+			enable_starpufft=$enableval,enable_starpufft=yes)
+
 PKG_CHECK_MODULES([FFTW],  [fftw3],  [
   AC_DEFINE([STARPU_HAVE_FFTW], [1], [Define to 1 if you have the libfftw3 library.])
   AC_SUBST([STARPU_HAVE_FFTW], [1])
@@ -1358,7 +1362,7 @@ PKG_CHECK_MODULES([FFTWL], [fftw3l], [
 ], [:])
 AM_CONDITIONAL(STARPU_HAVE_FFTWL, [test x$have_fftwl = xyes])
 
-if test \( x$enable_cpu = xyes -a x$have_fftw = xyes -a x$have_fftwf = xyes \) -o x$have_cufftdoublecomplex = xyes; then
+if test x$enable_starpufft = xyes -a \( \( x$enable_cpu = xyes -a x$have_fftw = xyes -a x$have_fftwf = xyes \) -o x$have_cufftdoublecomplex = xyes \); then
    fft_support=yes
 fi
 AM_CONDITIONAL(BUILD_STARPUFFT, [test x$fft_support = xyes])

doc/chapters/configuration.texi

@@ -167,6 +167,7 @@ device. It is then available as the @code{STARPU_MAXIMPLEMENTATIONS} macro.
 * --enable-allocation-cache::   
 * --enable-opengl-render::      
 * --enable-blas-lib::           
+* --disable-starpufft::           
 * --with-magma::                
 * --with-fxt::                  
 * --with-perf-model-dir::       
@@ -209,6 +210,10 @@ Enable the use of OpenGL for the rendering of some examples.
 Specify the blas library to be used by some of the examples. The
 library has to be 'atlas' or 'goto'.
 
+@node --disable-starpufft
+@subsubsection @code{--disable-starpufft}
+Disable the build of libstarpufft, even if fftw or cuFFT is available.
+
 @node --with-magma
 @subsubsection @code{--with-magma=<path>}
 Specify where magma is installed. This directory should notably contain