Allow NIX_* environment variables to be passed to rustc (#466)

Summary:
Otherwise if you are running buck2, and by extension rustc, from within nix any C(++) builds will fail.

All credit to fnichol who pointed me to [this fix in their prelude](https://github.com/systeminit/si/blob/main/prelude/rust/tools/rustc_action.py#L262).

Let me know if this fix is better applied somewhere else.

Pull Request resolved: #466

Reviewed By: dtolnay

Differential Revision: D66988964

Pulled By: IanChilds

fbshipit-source-id: 09752aac79527993a10bb79523179ca2d4ff6d97

prelude/rust/tools/rustc_action.py

@@ -30,6 +30,39 @@
 
 DEBUG = False
 
+NIX_ENV_VARS = [
+    "NIX_BINTOOLS",
+    "NIX_BINTOOLS_FOR_TARGET",
+    "NIX_CC",
+    "NIX_CC_FOR_TARGET",
+    "NIX_CFLAGS_COMPILE",
+    "NIX_CFLAGS_COMPILE_FOR_TARGET",
+    "NIX_COREFOUNDATION_RPATH",
+    "NIX_DONT_SET_RPATH",
+    "NIX_DONT_SET_RPATH_FOR_BUILD",
+    "NIX_ENFORCE_NO_NATIVE",
+    "NIX_HARDENING_ENABLE",
+    "NIX_IGNORE_LD_THROUGH_GCC",
+    "NIX_LDFLAGS",
+    "NIX_LDFLAGS_FOR_TARGET",
+    "NIX_NO_SELF_RPATH",
+]
+NIX_ENV_VAR_PREFIXES = [
+    "NIX_BINTOOLS_WRAPPER_TARGET_HOST_",
+    "NIX_BINTOOLS_WRAPPER_TARGET_TARGET_",
+    "NIX_CC_WRAPPER_TARGET_HOST_",
+    "NIX_CC_WRAPPER_TARGET_TARGET_",
+]
+
+
+def nix_env(env: Dict[str, str]):
+    env.update({k: os.environ[k] for k in NIX_ENV_VARS if k in os.environ})
+    for prefix in NIX_ENV_VAR_PREFIXES:
+        vars_starting_with = dict(
+            filter(lambda pair: pair[0].startswith(prefix), os.environ.items())
+        )
+        env.update(vars_starting_with.items())
+
 
 def eprint(*args: Any, **kwargs: Any) -> None:
     print(*args, end="\n", file=sys.stderr, flush=True, **kwargs)
@@ -281,6 +314,7 @@ async def main() -> int:  # noqa: C901
         ]
         if k in os.environ
     }
+    nix_env(env)
     if args.env:
         # Unescape previously escaped newlines.
         # Example: \\\\n\\n -> \\\n\n -> \\n\n