pw_build: Move "-Wcast-qual" to strict_warnings

Moves "-Wcast-qual" from extra_strict_warnings to strict_warnings.

Change-Id: Iab39c765c5222e6d6cbeac4933fd89874d06c695
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/21660
Reviewed-by: Ewout van Bekkum <ewout@google.com>
Reviewed-by: Wyatt Hepler <hepler@google.com>
Commit-Queue: Ewout van Bekkum <ewout@google.com>
diff --git a/pw_build/BUILD.gn b/pw_build/BUILD.gn
index 61b57c5..26a7f50 100644
--- a/pw_build/BUILD.gn
+++ b/pw_build/BUILD.gn
@@ -71,6 +71,7 @@
     "-Wall",
     "-Wextra",
     "-Wimplicit-fallthrough",
+    "-Wcast-qual",
 
     # Make all warnings errors, except for the exemptions below.
     "-Werror",
@@ -84,12 +85,7 @@
 # enable, but are enabled for upstream Pigweed for maximum project
 # compatibility.
 config("extra_strict_warnings") {
-  cflags = [
-    "-Wshadow",
-
-    # Migrate the warning(s) below to strict_warnings once customers support it.
-    "-Wcast-qual",
-  ]
+  cflags = [ "-Wshadow" ]
 }
 
 config("cpp11") {