Use the canonical TemplateDecl

...in case there are multiple, as is the case at least with recent (towards
GCC 8) libstdc++, where std::pair is forward-declared also in
include/c++/8.0.0/bits/stl_iterator.h, so that in
dbaccess/source/ui/dlg/DbAdminImpl.cxx

    std::pair< Reference<XConnection>,sal_Bool> aRet;
    aRet.second = false;

failed to reconstruct the sal_Bool template argument and issued a
loplugin:implicitboolconversion warning.

Change-Id: I0054f2596d3f8837b857f1dca2f25952828b12cc
Reviewed-on: https://gerrit.libreoffice.org/45254Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

compilerplugins/clang/implicitboolconversion.cxx

@@ -159,6 +159,7 @@ bool isBoolExpr(Expr const * expr) {
                 if (td == nullptr) {
                     break;
                 }
+                td = cast<TemplateDecl>(td->getCanonicalDecl());
                 TemplateParameterList const * ps = td->getTemplateParameters();
                 SubstTemplateTypeParmType const * t2
                     = getAsSubstTemplateTypeParmType(