VS: Place per-source preprocessor definitions after target-wide ones

When the VS 2010+ generators were first implemented in commit 7491f52992
(ENH: first pass at VS 10, can bootstrap CMake, but many tests still
fail, 2009-06-25, v2.8.0~546), the per-source preprocessor definitions
were placed before target-wide preprocessor definitions for consistency
with the behavior of VS 9 2008 and below.  However, those generators
are not used much anymore.  Instead prefer consistency with the order
used by the Ninja and Makefile generators.