Suppress error about unused -c argument

Clang now complains about the -c argument that Soong implicitly adds
before the -E argument.

Bug: http://b/379133546
Test: presubmit
Change-Id: Ie34f8d462005bc405cd1c752cb71a818d70e9477

diff --git a/libc/Android.bp b/libc/Android.bp
index 4f5b7e2..54bd8f4 100644
--- a/libc/Android.bp
+++ b/libc/Android.bp
@@ -2275,6 +2275,9 @@
         "-E",
         "-Wall",
         "-Werror",
+        // Soong implicitly adds a -c argument that we override with -E.
+        // Suppress Clang's error about the unused -c argument.
+        "-Wno-unused-command-line-argument",
         "-nostdinc",
     ],
 }