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, 2 insertions, 2 deletions

diff --git a/mesonbuild/envconfig.py b/mesonbuild/envconfig.py
index ac13a71..e0d07c5 100644
--- a/mesonbuild/envconfig.py
+++ b/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
-        ([] if is_cross else [var_name]),
+        [var_name],
     )[for_machine]
     for var in candidates:
         value = os.environ.get(var)