The given reason for needing to define it was that there was no way to
test whether <valgrind/valgrind.h> is available to #include; but we
now require C++17 hence __has_include(). However, moc doesn't seem to
grok that, so move the test's #if-ery inside the test, since otherwise
it gets omitted because the test's metatype doesn't know it's there.
Change-Id: I75a100787b98a52fad4cfb0b047318a115c998e2
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>