preprocessor: Miscellaneous cleanups

- Use full header paths in includes
- Use ASSERT instead of assert
- Use angle::NonCopyable instead of PP_DISALLOW_COPY_AND_ASSIGN
- Use range-for in a couple places
- Remove pp_utils.h

BUG=angleproject:1522

Change-Id: If107fef89e8465bca65cf664926d1051c5d1e232
Reviewed-on: https://chromium-review.googlesource.com/387212
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
diff --git a/src/compiler/preprocessor/DiagnosticsBase.cpp b/src/compiler/preprocessor/DiagnosticsBase.cpp
index 3281206..fcb24e4 100644
--- a/src/compiler/preprocessor/DiagnosticsBase.cpp
+++ b/src/compiler/preprocessor/DiagnosticsBase.cpp
@@ -4,9 +4,9 @@
 // found in the LICENSE file.
 //
 
-#include "DiagnosticsBase.h"
+#include "compiler/preprocessor/DiagnosticsBase.h"
 
-#include <cassert>
+#include "common/debug.h"
 
 namespace pp
 {
@@ -31,7 +31,7 @@
     if ((id > PP_WARNING_BEGIN) && (id < PP_WARNING_END))
         return PP_WARNING;
 
-    assert(false);
+    UNREACHABLE();
     return PP_ERROR;
 }
 
@@ -133,8 +133,8 @@
         return "macro name with a double underscore is reserved - unintented behavior is possible";
       // Warnings end.
       default:
-        assert(false);
-        return "";
+          UNREACHABLE();
+          return "";
     }
 }