Enable -Wshadow and -Wunreachable-code-aggressive under nacl/saigo

The nacl saigo toolchain supports many things the old nacl toolchains
don't.

Similar to https://chromium-review.googlesource.com/c/chromium/src/+/3261253

Depends on:
https://chromium-review.googlesource.com/c/native_client/src/native_client/+/3296267
https://chromium-review.googlesource.com/c/native_client/src/native_client/+/3296095

Bug: 1106311,794619,346399
Change-Id: I7d3c0d8fc8c42ecdd89b6c581af65726f26bec01
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3298490
Auto-Submit: Nico Weber <thakis@chromium.org>
Commit-Queue: Hans Wennborg <hans@chromium.org>
Reviewed-by: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/main@{#944964}
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index d6b95436..db71cd5 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -1601,7 +1601,7 @@
 
     # TODO(thakis): Enable this more often, https://crbug.com/346399
     # use_libfuzzer: https://crbug.com/1063180
-    if (!is_nacl && !use_libfuzzer) {
+    if ((!is_nacl || is_nacl_saigo) && !use_libfuzzer) {
       cflags += [ "-Wunreachable-code-aggressive" ]
     }
 
@@ -1691,7 +1691,7 @@
 config("noshadowing") {
   # This flag has to be disabled for nacl because the nacl compiler is too
   # strict about shadowing.
-  if (is_clang && !is_nacl) {
+  if (is_clang && (!is_nacl || is_nacl_saigo)) {
     cflags = [ "-Wshadow" ]
   }
 }