Revert "Naturally use env vars a bit more to match Autoconf"

This reverts commit 097dfc085e.

docs/markdown/howtox.md

@@ -12,16 +12,15 @@ When first running Meson, set it in an environment variable.
 $ CC=mycc meson <options>
 ```
 
-Note that environment variables like `CC` only refer to the host platform in
-cross builds.  That is, the `CC` refers 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 always used `CC_FOR_BUILD`, but for native builds
-it is less well known because Meson (and Autotools) will default `CC_FOR_BUILD`
-with `CC`.
+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 are never the idiomatic way to do anything with
-Meson, however. It is better to use the native and cross files.
+Meson, however. It is better to use the native and cross files. And the tools
+for the host platform in cross builds can only be specified with a cross file.
 
 There is a table of all environment variables supported [Here](Reference-tables.md#compiler-and-linker-selection-variables)
 

docs/markdown/snippets/env_vars_and_cross.md

@@ -2,11 +2,11 @@
 
 Previously in Meson, variables like `CC` effected both the host and build
 platforms for native builds, but the just the build platform for cross builds.
-Now `CC` always effects the host platform, and `CC_FOR_BUILD` always affects
-the build platform, with `CC` also effecting the build platform for native
-builds only when `CC_FOR_BUILD` is not defined.
+Now `CC_FOR_BUILD` is used for the build platform in cross builds.
 
 This old behavior is inconsistent with the way Autotools works, which
 undermines the purpose of distro-integration that is the only reason
-environment variables are supported at all in Meson. The new behavior is
-consistent.
+environment variables are supported at all in Meson. The new behavior is not
+quite the same, but doesn't conflict: meson doesn't always repond to an
+environment when Autoconf would, but when it does it interprets it as Autotools
+would.

mesonbuild/envconfig.py

@@ -119,9 +119,9 @@ def get_env_var_pair(for_machine: MachineChoice,
         # compiling we fall back on the unprefixed host version. This
         # allows native builds to never need to worry about the 'BUILD_*'
         # ones.
-        [var_name + '_FOR_BUILD'] + ([] if is_cross else [var_name]),
+        ([var_name + '_FOR_BUILD'] if is_cross else [var_name]),
         # Always just the unprefixed host verions
-        [var_name],
+        ([] if is_cross else [var_name]),
     )[for_machine]
     for var in candidates:
         value = os.environ.get(var)

run_unittests.py

@@ -6338,10 +6338,11 @@ c = ['{0}']
         testdir = os.path.join(self.unit_test_dir, '61 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('')
+        crossfile.write('''[binaries]
+c = ['{0}']
+'''.format(os.path.join(testdir, 'host_wrapper.py')))
         crossfile.flush()
         self.meson_cross_file = crossfile.name
         # TODO should someday be explicit about build platform only here