Bump --enable-compiler-plugins to Clang 3.8.0

<https://lists.freedesktop.org/archives/libreoffice/2017-December/079107.html>
"Clang baseline bump"

Change-Id: I18fca8794ea34118fc6308458064d0c28cf5caf7
Reviewed-on: https://gerrit.libreoffice.org/46557
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

compilerplugins/clang/datamembershadow.cxx

@@ -100,8 +100,6 @@ bool DataMemberShadow::VisitFieldDecl(FieldDecl const * fieldDecl)
 
     fieldDecl = fieldDecl->getCanonicalDecl();
 
-#if CLANG_VERSION >= 30800
-
     auto BaseMatchesCallback = [&](const CXXBaseSpecifier *cxxBaseSpecifier, CXXBasePath& Paths)
     {
         if (!cxxBaseSpecifier->getType().getTypePtr())
@@ -143,7 +141,6 @@ bool DataMemberShadow::VisitFieldDecl(FieldDecl const * fieldDecl)
 
     CXXBasePaths aPaths;
     parentCXXRecordDecl->lookupInBases(BaseMatchesCallback, aPaths);
-#endif
     return true;
 }