bitbake: utils: add environment updating context manager

bb.utils.environment() is a context manager to alter os.environ inside
a specific block, restoring it after the block is closed.

(Bitbake rev: 9974848f67581ff7d76cef52a94f505af99b4932)

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/utils.py

@@ -1681,3 +1681,19 @@ def rename(src, dst):
             shutil.move(src, dst)
         else:
             raise err
+
+@contextmanager
+def environment(**envvars):
+    """
+    Context manager to selectively update the environment with the specified mapping.
+    """
+    backup = dict(os.environ)
+    try:
+        os.environ.update(envvars)
+        yield
+    finally:
+        for var in envvars:
+            if var in backup:
+                os.environ[var] = backup[var]
+            else:
+                del os.environ[var]