environment, env2mfile: Don't shell split paths if they point to a valid executable

Fixes #11128

mesonbuild/environment.py

@@ -747,6 +747,9 @@ class Environment:
         for (name, evar), for_machine in itertools.product(opts, MachineChoice):
             p_env = _get_env_var(for_machine, self.is_cross_build(), evar)
             if p_env is not None:
+                if os.path.exists(p_env):
+                    self.binaries[for_machine].binaries.setdefault(name, [p_env])
+                else:
                     self.binaries[for_machine].binaries.setdefault(name, mesonlib.split_args(p_env))
 
     def _set_default_properties_from_env(self) -> None:

mesonbuild/scripts/env2mfile.py

@@ -296,6 +296,9 @@ def detect_compilers_from_envvars(envvar_suffix: str = '') -> MachineInfo:
         compilerstr = os.environ.get(envvarname + envvar_suffix)
         if not compilerstr:
             continue
+        if os.path.exists(compilerstr):
+            compiler = [compilerstr]
+        else:
             compiler = shlex.split(compilerstr)
         infos.compilers[langname] = compiler
         lang_compile_args, lang_link_args = detect_language_args_from_envvars(langname, envvar_suffix)