stm32cube: Fix H7 build

Ignores two more warnings to get H7 to build.
Verified by building and running binary on H7 board.

Change-Id: Ibc3ad4819dd78efadc579fcfddb32c49436de0ed
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/55048
Reviewed-by: Ali Zhang <alizhang@google.com>
Commit-Queue: Varun Sharma <vars@google.com>
diff --git a/third_party/stm32cube/BUILD.gn b/third_party/stm32cube/BUILD.gn
index b97bd87..6df0eb6 100644
--- a/third_party/stm32cube/BUILD.gn
+++ b/third_party/stm32cube/BUILD.gn
@@ -111,6 +111,8 @@
     "-Wno-sign-compare",
     "-Wno-old-style-declaration",
     "-Wno-maybe-uninitialized",
+    "-Wno-undef",
+    "-Wno-implicit-function-declaration",
   ]
   defines = [
     "USE_HAL_DRIVER",