Naturally use env vars a bit more to match Autoconf

PR #6363 made it so our interpretation of env vars no longer clashed
with Autoconf's: if both Meson and Autoconf would read and env var, both
would do the same things with the value they read.

However, there were still cases that autoconf would read an env var when
meson wouldn't:

 - Autoconf would use `CC` in cross builds too

 - Autoconf would use `CC_FOR_BUILD` in native builds too.

There's no reason Meson can't also do this--if native cross files
overwrite rather than replace env vars, cross files can also overwrite
rather than replace env vars.

Because variables like `CC` are so ubiquitous, and because ignoring them
in cross builds just makes those builds liable to break (and things more
complicated in general), we bring Meson's behavior in line with
Autoconf's.

1 files changed, 8 insertions, 7 deletions

diff --git a/docs/markdown/howtox.md b/docs/markdown/howtox.md
index 8231d3d..ee7fc9c 100644
--- a/docs/markdown/howtox.md
+++ b/docs/markdown/howtox.md
@@ -12,15 +12,16 @@ 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, 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 are never the idiomatic way to do anything with
-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.
+Meson, however. It is better to use the native and cross files.
 
 There is a table of all environment variables supported [Here](Reference-tables.md#compiler-and-linker-selection-variables)