Add amgx (#16357)

* add amgx package

* add amgx variants for mkl and magma support

* fix typo in cmake option

* flake8 fix formatting

* Apply suggestions from code review - use mkl virtual provider

Co-Authored-By: Adam J. Stewart <ajstewart426@gmail.com>

* Apply suggestions from code review - fix copypasta

Co-Authored-By: Adam J. Stewart <ajstewart426@gmail.com>

Co-authored-by: Adam J. Stewart <ajstewart426@gmail.com>

var/spack/repos/builtin/packages/amgx/package.py

@@ -0,0 +1,58 @@
+# Copyright 2013-2020 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 Amgx(CMakePackage, CudaPackage):
+    """AmgX provides a simple path to accelerated core solver technology on
+    NVIDIA GPUs. AmgX provides up to 10x acceleration to the computationally
+    intense linear solver portion of simulations, and is especially well
+    suited for implicit unstructured methods. It is a high performance,
+    state-of-the-art library and includes a flexible solver composition
+    system that allows a user to easily construct complex nested solvers and
+    preconditioners."""
+
+    homepage = "https://developer.nvidia.com/amgx"
+    url      = "https://github.com/nvidia/amgx/archive/v2.1.0.tar.gz"
+
+    maintainers = ['js947']
+
+    version('2.1.0', sha256='6245112b768a1dc3486b2b3c049342e232eb6281a6021fffa8b20c11631f63cc')
+    version('2.0.1', sha256='6f9991f1836fbf4ba2114ce9f49febd0edc069a24f533bd94fd9aa9be72435a7')
+    version('2.0.0', sha256='8ec7ea8412be3de216fcf7243c4e2a8bcf76878e6865468e4238630a082a431b')
+
+    variant('cuda', default=True, description='Build with CUDA')
+    variant('mpi', default=True, description='Enable MPI support')
+    variant('mkl', default=False, description='Enable MKL support')
+    variant('magma', default=False, description='Enable Magma support')
+
+    depends_on('mpi', when='+mpi')
+    depends_on('mkl', when='+mkl')
+    depends_on('magma', when='+magma')
+
+    def cmake_args(self):
+        args = []
+        args.append("-DCMAKE_NO_MPI={0}".format(
+            '1' if '+mpi' not in self.spec else '0'))
+
+        if '+cuda' in self.spec:
+            args.append('-DWITH_CUDA=ON')
+            cuda_arch = self.spec.variants['cuda_arch'].value
+            if cuda_arch is not None:
+                args.append('-DCUDA_ARCH={0}'.format(cuda_arch[0]))
+        else:
+            args.append('-DWITH_CUDA=OFF')
+
+        if '+mkl' in self.spec:
+            args.append('-DMKL_ROOT_DIR={0}'.format(
+                self.spec['mkl'].prefix))
+
+        if '+magma' in self.spec:
+            args.append('-DMAGMA_ROOT_DIR={0}'.format(
+                self.spec['magma'].prefix))
+
+        return args