fix(py-flit-core): copy package from upstream

packages/py-flit-core/package.py

+# 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 PyFlitCore(PythonPackage):
+    """Distribution-building parts of Flit."""
+
+    homepage = "https://github.com/pypa/flit"
+    pypi = "flit-core/flit_core-3.9.0.tar.gz"
+    maintainers("takluyver")
+
+    version("3.9.0", sha256="72ad266176c4a3fcfab5f2930d76896059851240570ce9a98733b658cb786eba")
+    version("3.8.0", sha256="b305b30c99526df5e63d6022dd2310a0a941a187bd3884f4c8ef0418df6c39f3")
+    version("3.7.1", sha256="14955af340c43035dbfa96b5ee47407e377ee337f69e70f73064940d27d0a44f")
+    version("3.6.0", sha256="5892962ab8b8ea945835b3a288fe9dd69316f1903d5288c3f5cafdcdd04756ad")
+    version("3.5.1", sha256="3083720351a6cb00e0634a1ec0e26eae7b273174c3c6c03d5b597a14203b282e")
+    version("3.5.0", sha256="2db800d33ff41e4c6e7c1b594666cb2a11553024106655272c7245933b1d75bd")
+    version("3.4.0", sha256="29468fa2330969167d1f5c23eb9c0661cb6dacfcd46f361a274609a7f4197530")
+    version("3.3.0", sha256="b1404accffd6504b5f24eeca9ec5d3c877f828d16825348ba81515fa084bd5f0")
+    version("3.2.0", sha256="ff87f25c5dbc24ef30ea334074e35030e4885e4c5de3bf4e21f15746f6d99431")
+    version("3.1.0", sha256="22ff73be39a2b3c9e0692dfbbea3ad4a9d127e5733736a87dbb8ddcbf7309b1e")
+    version("3.0.0", sha256="a465052057e2d6d957e6850e9915245adedfc4fd0dd5737d0791bf3132417c2d")
+    version("2.3.0", sha256="a50bcd8bf5785e3a7d95434244f30ba693e794c5204ac1ee908fc07c4acdbf80")
+
+    # pyproject.toml
+    depends_on("python@3.6:", when="@3.4:", type=("build", "run"))
+    depends_on("python@3.4:", when="@3:", type=("build", "run"))
+    depends_on("python@2.7,3.4:", type=("build", "run"))
+
+    # flit_core/build_thyself.py
+    depends_on("py-tomli", when="@3.4:3.5", type="run")
+    depends_on("py-toml", when="@3.1:3.3", type="run")
+    depends_on("py-pytoml", when="@:3.0", type="run")