gnu: macs: Remove generated code.

* gnu/packages/bioinformatics.scm (macs)[source]: Add snippet to remove
cython generated code.
[native-inputs]: Add python-cython.

gnu/packages/bioinformatics.scm

@@ -4475,7 +4475,19 @@ experiments.")
               (file-name (git-file-name name version))
               (sha256
                (base32
-                "1c5gxr0mk6hkd4vclf0k00wvyvzw2vrmk52c85338p7aqjwg6n15"))))
+                "1c5gxr0mk6hkd4vclf0k00wvyvzw2vrmk52c85338p7aqjwg6n15"))
+        (modules '((guix build utils)))
+        ;; Remove files generated by Cython
+        (snippet
+         '(begin
+            (for-each (lambda (file)
+                        (let ((generated-file
+                                (string-append (string-drop-right file 3) "c")))
+                          (when (file-exists? generated-file)
+                            (delete-file generated-file))))
+                      (find-files "." "\\.pyx$"))
+            (delete-file "MACS2/IO/CallPeakUnitPrecompiled.c")
+            #t))))
     (build-system python-build-system)
     (arguments
      `(#:phases
@@ -4489,7 +4501,8 @@ experiments.")
     (inputs
      `(("python-numpy" ,python-numpy)))
     (native-inputs
-     `(("python-pytest" ,python-pytest)))
+     `(("python-cython" ,python-cython)
+       ("python-pytest" ,python-pytest)))
     (home-page "https://github.com/macs3-project/MACS")
     (synopsis "Model based analysis for ChIP-Seq data")
     (description