Add cmake package for v2.1.0 and master (git) versions of libfirefly (#39778)

* libfirefly: Add cmake package for v2.1.0 and master (git) versions

* Separate git URL from version declaration

Co-authored-by: Alec Scott <alec@bcs.sh>

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

@@ -0,0 +1,29 @@
+# Copyright 2013-2023 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.package import *
+
+
+class Libfirefly(CMakePackage):
+    """A standalone C++ Library for vectors calculations"""
+
+    homepage = "https://libfirefly.tbhaxor.com"
+    url = "https://github.com/tbhaxor/firefly/archive/refs/tags/v2.1.0.tar.gz"
+    git = "https://github.com/tbhaxor/firefly.git"
+
+    maintainers("tbhaxor")
+
+    version("master", branch="master")
+    version("2.1.0", sha256="4de4b216c73199a1826de7a0d45205b401603315347d7947d8b5950d3e6b893d")
+
+    variant(
+        "double-precision",
+        description="Enables double type instead of float when enabled",
+        default=True,
+    )
+
+    def cmake_args(self):
+        args = [self.define_from_variant("Firefly_ENABLE_DOUBLE_PRECISION", "double-precision")]
+        return args