Disable valgrind detection when compiling with MSVC
Summary: MSVC chokes on the inline assembly, use the stub macros there instead.
Test Plan:
Valgrind detection on Linux/GCC still works
MSVC untested
Reviewers: Windows, bcooksley
Reviewed By: Windows
Subscribers: Baloo, alexeymin, kde-frameworks-devel
Tags: Frameworks, Baloo
Differential Revision: https://phabricator.kde.org/D21599