Bump impeller-cmake to HEAD
diff --git a/third_party/impeller-cmake b/third_party/impeller-cmake
index fd07867..42fa252 160000
--- a/third_party/impeller-cmake
+++ b/third_party/impeller-cmake
@@ -1 +1 @@
-Subproject commit fd07867693a7dfd7cbcff5212fcd60c149f9363a
+Subproject commit 42fa25249bb23e87ec0f1b472d2318b92ca91cef