Suppress warnings while testing a new compiler

The -Wmacro-redefined warning causes a build failure after building the
musl libc++ with the LIBCXX_HAS_MUSL_LIBC CMake var
(r.android.com/3355477).

Bug: http://b/379357589
Test: treehugger
Change-Id: I8b4f6f659609effef9fb283167c578f6b1d7ed9b

diff --git a/rust/bindgen.go b/rust/bindgen.go
index 3944495..f792925 100644
--- a/rust/bindgen.go
+++ b/rust/bindgen.go
@@ -300,6 +300,11 @@
 	// it cannot recognize. Turn off unknown warning flags warning.
 	cflags = append(cflags, "-Wno-unknown-warning-option")
 
+	// Suppress warnings while testing a new compiler.
+	if ctx.Config().IsEnvTrue("LLVM_NEXT") {
+		cflags = append(cflags, "-Wno-everything")
+	}
+
 	outputFile := android.PathForModuleOut(ctx, b.BaseSourceProvider.getStem(ctx)+".rs")
 
 	var cmd, cmdDesc string