Document and test env vars a bit better

docs/markdown/howtox.md

@@ -12,12 +12,12 @@ When first running Meson, set it in an environment variable.
 $ CC=mycc meson <options>
 ```
 
-Note that environment variables like `CC` only works in native builds.
-The `CC` refers to the compiler for the host platform, that is the
-compiler used to compile programs that run on the machine we will
-eventually install the project on. The compiler used to build things
-that run on the machine we do the building can be specified with
-`CC_FOR_BUILD`. You can use it in cross builds.
+Note that environment variables like `CC` only refer to the host
+platform in cross builds.  That is, `CC` refers to the compiler used to
+compile programs that run on the machine we will eventually install the
+project on. The compiler used to build things that run on the machine we
+do the building can be specified with `CC_FOR_BUILD`. You can use it in
+cross builds.
 
 Note that environment variables are never the idiomatic way to do
 anything with Meson, however. It is better to use the native and cross

unittests/linuxliketests.py

@@ -1545,12 +1545,10 @@ def test_identity_cross_env(self):
         testdir = os.path.join(self.unit_test_dir, '60 identity cross')
         env = {
             'CC_FOR_BUILD': '"' + os.path.join(testdir, 'build_wrapper.py') + '"',
+            'CC': '"' + os.path.join(testdir, 'host_wrapper.py') + '"',
         }
         crossfile = tempfile.NamedTemporaryFile(mode='w')
-        crossfile.write(textwrap.dedent('''\
-            [binaries]
-            c = ['{}']
-            '''.format(os.path.join(testdir, 'host_wrapper.py'))))
+        crossfile.write('')
         crossfile.flush()
         self.meson_cross_files = [crossfile.name]
         # TODO should someday be explicit about build platform only here