meson: Clearly print error when distutils or packaging is missing

Previously, if neither packaging.version or distutils.version is present
in the environment the has_mako check would return non-zero exit code
and meson would print that mako is required which is misleading since
mako can be in the environment but not packaging or distutils. This can
happen for Python>=3.12 where distutils is no longer in the Python
stdlib but provided externally by setuptools.

Signed-off-by: bbhtt <bbhtt.zn0i8@slmail.me>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36697>

meson.build

@@ -924,15 +924,29 @@ prog_python = find_program('python3', 'python', version : '>= 3.9')
 has_mako = run_command(
   prog_python, '-c',
   '''
+import sys
+
 try:
-  from packaging.version import Version
+    try:
+        from packaging.version import Version
+    except:
+        from distutils.version import StrictVersion as Version
 except:
-  from distutils.version import StrictVersion as Version
-import mako
-assert Version(mako.__version__) >= Version("0.8.0")
-  ''', check: false)
-if has_mako.returncode() != 0
+    sys.exit(2)
+
+try:
+    import mako
+except:
+    sys.exit(1)
+
+if Version(mako.__version__) < Version("0.8.0"):
+    sys.exit(1)
+''', check: false)
+
+if has_mako.returncode() == 1
   error('Python (3.x) mako module >= 0.8.0 required to build mesa.')
+elif has_mako.returncode() == 2
+  error('One of Python (3.x) packaging or distutils module is required.')
 endif
 
 has_yaml = run_command(