Add cray-fftw (#20654)

var/spack/repos/builtin/packages/cray-fftw/package.py

@@ -0,0 +1,34 @@
+# Copyright 2013-2021 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+from spack import *
+
+
+class CrayFftw(Package):
+    """FFTW is a C subroutine library for computing the discrete Fourier
+       transform (DFT) in one or more dimensions, of arbitrary input
+       size, and of both real and complex data (as well as of even/odd
+       data, i.e. the discrete cosine/sine transforms or DCT/DST).
+       This package is a wrapper for Cray's version of FFTW.
+
+       To install this package, list it as an external package in packages.yaml,
+       and make sure to load the correct cray-fftw module. In some cases you
+       need to load cray-mpich before cray-fftw.
+       """
+
+    homepage = "https://docs.nersc.gov/development/libraries/fftw/"
+    has_code = False    # Skip attempts to fetch source that is not available
+
+    maintainers = ['haampie']
+
+    version('3.3.8.8')
+    version('3.3.8.7')
+
+    provides('fftw-api@3')
+
+    def install(self, spec, prefix):
+        raise InstallError(
+            self.spec.format('{name} is not installable, you need to specify '
+                             'it as an external package in packages.yaml'))