texinfo package: fix external detection (#40470)

A complete texinfo install includes both `info` and `makeinfo`. Some
system installations of texinfo may exclude one or the other. This
updates the external finding logic to require both.

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

@@ -3,6 +3,7 @@
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
+import os
 import re
 
 from spack.package import *
@@ -69,6 +70,13 @@ def setup_build_environment(self, env):
 
     @classmethod
     def determine_version(cls, exe):
+        # On CentOS and Ubuntu, the OS package info installs "info",
+        # which satisfies spack external find, but "makeinfo" comes
+        # from texinfo and may not be installed (and vice versa).
+        (texinfo_path, info_exe) = os.path.split(exe)
+        makeinfo_exe = os.path.join(texinfo_path, "makeinfo")
+        if not os.path.exists(makeinfo_exe):
+            return None
         output = Executable(exe)("--version", output=str, error=str)
         match = re.search(r"info \(GNU texinfo\)\s+(\S+)", output)
         return match.group(1) if match else None