v2.1.0

deps: match Abseil's MSVC runtime to ossia's

Abseil's CMakeLists overrides CMAKE_MSVC_RUNTIME_LIBRARY from its own
ABSL_MSVC_STATIC_RUNTIME option (default OFF -> /MD dynamic), ignoring the
runtime selected by the enclosing build. Static ossia builds (Max/PD/Python/
Unity) force the static /MT runtime, so Abseil's /MD objects fail to link:

  absl_*.lib(...) : error LNK2038: mismatch detected for 'RuntimeLibrary':
  value 'MD_DynamicRelease' doesn't match value 'MT_StaticRelease'

Set ABSL_MSVC_STATIC_RUNTIME to mirror CMAKE_MSVC_RUNTIME_LIBRARY so the two
agree.