tools build: Fix test-clang.cpp with Clang 8+

LLVM rL344140 (included in Clang 8+) moved VFS from Clang to LLVM, so
paths to its include files have changed.

This broke the Clang test in tools/build - let's fix it.

Signed-off-by: Maciej S. Szmigiero <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Denis Pronin <[e-mail]>
Cc: Dennis Schridde <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Naohiro Aota <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: [e-mail]
Link: http://lore.kernel.org/lkml/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/build/feature/test-clang.cpp

···
 // SPDX-License-Identifier: GPL-2.0
+#include "clang/Basic/Version.h"
+#if CLANG_VERSION_MAJOR < 8
 #include "clang/Basic/VirtualFileSystem.h"
+#endif
 #include "clang/Driver/Driver.h"
 #include "clang/Frontend/TextDiagnosticPrinter.h"
 #include "llvm/ADT/IntrusiveRefCntPtr.h"
 #include "llvm/Support/ManagedStatic.h"
+#if CLANG_VERSION_MAJOR >= 8
+#include "llvm/Support/VirtualFileSystem.h"
+#endif
 #include "llvm/Support/raw_ostream.h"
 
 using namespace clang;