Use an amd64 Debian Buster sysroot for building

One of the transitive opencv dependencies needs the newer libc.

Change-Id: I4964bc753aa0dc51c9481896354e272c13a164d5
diff --git a/tools/cpp/clang_6p0/clang_6p0.BUILD b/tools/cpp/clang_6p0/clang_6p0.BUILD
index e70f8a9..ef674c9 100644
--- a/tools/cpp/clang_6p0/clang_6p0.BUILD
+++ b/tools/cpp/clang_6p0/clang_6p0.BUILD
@@ -88,13 +88,15 @@
 filegroup(
     name = "compiler_pieces",
     srcs = glob(
-        [
+        include = [
             "**",
         ],
         exclude = [
             "usr/share/**",
         ],
-    ),
+    ) + [
+        "@amd64_debian_sysroot//:sysroot_files",
+    ],
 )
 
 filegroup(