env2mfile: Use a cross valac on Debian if possible

This is functionally equivalent to the logic used to locate the cross
exe_wrapper, but puts it below the "Compilers" heading rather than
"Other binaries".

Signed-off-by: Simon McVittie <smcv@debian.org>

mesonbuild/scripts/env2mfile.py

@@ -250,6 +250,13 @@ def dpkg_architecture_to_machine_info(output: str, options: T.Any) -> MachineInf
             infos.binaries[tool] = locate_path("%s-%s" % (host_arch, exe))
         except ValueError:
             pass
+    for tool, exe in [
+        ('vala', 'valac'),
+    ]:
+        try:
+            infos.compilers[tool] = locate_path("%s-%s" % (host_arch, exe))
+        except ValueError:
+            pass
     try:
         infos.binaries['cups-config'] = locate_path("cups-config")
     except ValueError:

unittests/internaltests.py

@@ -1739,6 +1739,7 @@ class InternalTests(unittest.TestCase):
                 'cpp': [f'/usr/bin/{gnu_tuple}-g++{gcc_suffix}'],
                 'objc': [f'/usr/bin/{gnu_tuple}-gobjc{gcc_suffix}'],
                 'objcpp': [f'/usr/bin/{gnu_tuple}-gobjc++{gcc_suffix}'],
+                'vala': [f'/usr/bin/{gnu_tuple}-valac'],
             }
 
         def expected_binaries(gnu_tuple: str) -> T.Dict[str, T.List[str]]: