Do not report warnings when testing with the top of trunk LLVM

also clean up flags for Clang r475365.

Test: LLVM_NEXT=true m
Change-Id: I6ebbedc6b3e3adb50c156b852eb113a1c64ffc2a
diff --git a/cc/config/global.go b/cc/config/global.go
index c0f6e77..e78839b 100644
--- a/cc/config/global.go
+++ b/cc/config/global.go
@@ -294,8 +294,8 @@
 	}
 
 	llvmNextExtraCommonGlobalCflags = []string{
-		// New warnings to be fixed after clang-r475365
-		"-Wno-error=single-bit-bitfield-constant-conversion", // http://b/243965903
+		// Do not report warnings when testing with the top of trunk LLVM.
+		"-Wno-error",
 	}
 
 	IllegalFlags = []string{