shtools: New package (#15133)

* shtools: New package

* shtools: Convert to MakefilePackage, use Spack's generic compiler flags

* shtools: Make function location explicit

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

+# 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 Shtools(MakefilePackage):
+    """SHTOOLS - Spherical Harmonic Tools"""
+
+    homepage = "https://shtools.github.io/SHTOOLS/"
+    url      = "https://github.com/SHTOOLS/SHTOOLS/archive/v4.5.tar.gz"
+
+    maintainers = ['eschnett']
+
+    version('4.5', sha256='1975a2a2bcef8c527d321be08c13c2bc479e0d6b81c468a3203f95df59be4f89')
+
+    # Note: This package also provides Python wrappers. We do not
+    # install these properly yet, only the Fortran library is
+    # installed.
+
+    variant('openmp', default=True, description="Enable OpenMP support")
+
+    depends_on('blas')
+    depends_on('fftw')
+    depends_on('lapack')
+
+    # Options for the Makefile
+    def makeopts(self, spec, prefix):
+        return [
+            "F95={0}".format(self.compiler.fc),
+            ("F95FLAGS={0} -O3 -std=f2003 -ffast-math".
+             format(self.compiler.pic_flag)),
+            "OPENMPFLAGS={0}".format(self.compiler.openmp_flag),
+            "BLAS={0}".format(spec['blas'].libs),
+            "FFTW={0}".format(spec['fftw'].libs),
+            "LAPACK={0}".format(spec['lapack'].libs),
+            "PREFIX={0}".format(prefix),
+        ]
+
+    def build(self, spec, prefix):
+        target = 'fortran-mp' if spec.satisfies('+openmp') else 'fortran'
+        make(target, *self.makeopts(self, spec, prefix))
+
+    def install(self, spec, prefix):
+        make('install', *self.makeopts(self, spec, prefix))