threading: avoid defining _WIN32_WINNT
threading: avoid defining _WIN32_WINNT

The referenced function (SignalObjectAndWait) isn't used. Reduces the
warnings with mingw32-w64 which defines this.

Change-Id: I4ce592879ec9372bf196dac640204c4d370bd210

luctrudeau/aom,turbulenz/libvpx,thdav/aom,altogother/webm.libvpx,smarter/aom,kalli123/webm.libvpx,cinema6/libvpx,smarter/aom,vasilvv/esvp8,hsueceumd/test_hui,charup/https---github.com-webmproject-libvpx-,webmproject/libvpx,mwgoldsmith/vpx,ittiamvpx/libvpx,ittiamvpx/libvpx-1,WebRTC-Labs/libvpx,mwgoldsmith/vpx,webmproject/libvpx,jmvalin/aom,stewnorriss/libvpx,running770/libvpx,GrokImageCompression/aom,awatry/libvpx.opencl,abwiz0086/webm.libvpx,Laknot/libvpx,cinema6/libvpx,matanbs/webm.libvpx,jdm/libvpx,shyamalschandra/libvpx,jmvalin/aom,smarter/aom,cinema6/libvpx,jdm/libvpx,lyx2014/libvpx_c,zofuthan/libvpx,thdav/aom,gshORTON/webm.libvpx,Distrotech/libvpx,thdav/aom,openpeer/libvpx_new,GrokImageCompression/aom,VTCSecureLLC/libvpx,shareefalis/libvpx,felipebetancur/libvpx,mbebenita/aom,gshORTON/webm.libvpx,turbulenz/libvpx,kleopatra999/webm.libvpx,VTCSecureLLC/libvpx,openpeer/libvpx_new,jacklicn/webm.libvpx,charup/https---github.com-webmproject-libvpx-,jacklicn/webm.libvpx,stewnorriss/libvpx,gshORTON/webm.libvpx,goodleixiao/vpx,iniwf/webm.libvpx,matanbs/vp982,ittiamvpx/libvpx-1,shareefalis/libvpx,charup/https---github.com-webmproject-libvpx-,sanyaade-teachings/libvpx,ittiamvpx/libvpx-1,matanbs/webm.libvpx,stewnorriss/libvpx,matanbs/webm.libvpx,shyamalschandra/libvpx,webmproject/libvpx,shacklettbp/aom,running770/libvpx,Maria1099/webm.libvpx,felipebetancur/libvpx,matanbs/vp982,matanbs/vp982,ittiamvpx/libvpx,pcwalton/libvpx,mbebenita/aom,abwiz0086/webm.libvpx,jdm/libvpx,turbulenz/libvpx,Laknot/libvpx,felipebetancur/libvpx,ittiamvpx/libvpx,ittiamvpx/libvpx-1,altogother/webm.libvpx,shareefalis/libvpx,charup/https---github.com-webmproject-libvpx-,ittiamvpx/libvpx,matanbs/webm.libvpx,Suvarna1488/webm.libvpx,gshORTON/webm.libvpx,jdm/libvpx,awatry/libvpx.opencl,matanbs/vp982,charup/https---github.com-webmproject-libvpx-,Maria1099/webm.libvpx,Topopiccione/libvpx,kalli123/webm.libvpx,shacklettbp/aom,mbebenita/aom,sanyaade-teachings/libvpx,mwgoldsmith/libvpx,shacklettbp/aom,ShiftMediaProject/libvpx,cinema6/libvpx,n4t/libvpx,kim42083/webm.libvpx,abwiz0086/webm.libvpx,kleopatra999/webm.libvpx,iniwf/webm.libvpx,stewnorriss/libvpx,shacklettbp/aom,jacklicn/webm.libvpx,ittiamvpx/libvpx-1,webmproject/libvpx,mbebenita/aom,ittiamvpx/libvpx,stewnorriss/libvpx,shareefalis/libvpx,running770/libvpx,kalli123/webm.libvpx,hsueceumd/test_hui,iniwf/webm.libvpx,kim42083/webm.libvpx,hsueceumd/test_hui,turbulenz/libvpx,altogother/webm.libvpx,WebRTC-Labs/libvpx,running770/libvpx,shacklettbp/aom,smarter/aom,GrokImageCompression/aom,vasilvv/esvp8,mbebenita/aom,mwgoldsmith/vpx,felipebetancur/libvpx,abwiz0086/webm.libvpx,goodleixiao/vpx,jmvalin/aom,Maria1099/webm.libvpx,Maria1099/webm.libvpx,Suvarna1488/webm.libvpx,cinema6/libvpx,felipebetancur/libvpx,smarter/aom,abwiz0086/webm.libvpx,Acidburn0zzz/webm.libvpx,liqianggao/libvpx,thdav/aom,Maria1099/webm.libvpx,mbebenita/aom,jdm/libvpx,webmproject/libvpx,WebRTC-Labs/libvpx,thdav/aom,zofuthan/libvpx,shareefalis/libvpx,jacklicn/webm.libvpx,Suvarna1488/webm.libvpx,openpeer/libvpx_new,GrokImageCompression/aom,luctrudeau/aom,kim42083/webm.libvpx,liqianggao/libvpx,VTCSecureLLC/libvpx,luctrudeau/aom,mwgoldsmith/libvpx,goodleixiao/vpx,liqianggao/libvpx,awatry/libvpx.opencl,luctrudeau/aom,kim42083/webm.libvpx,shyamalschandra/libvpx,matanbs/vp982,pcwalton/libvpx,luctrudeau/aom,sanyaade-teachings/libvpx,Topopiccione/libvpx,Topopiccione/libvpx,zofuthan/libvpx,turbulenz/libvpx,jmvalin/aom,thdav/aom,n4t/libvpx,pcwalton/libvpx,zofuthan/libvpx,vasilvv/esvp8,GrokImageCompression/aom,altogother/webm.libvpx,smarter/aom,stewnorriss/libvpx,Distrotech/libvpx,openpeer/libvpx_new,ShiftMediaProject/libvpx,Distrotech/libvpx,goodleixiao/vpx,Acidburn0zzz/webm.libvpx,pcwalton/libvpx,turbulenz/libvpx,altogother/webm.libvpx,shareefalis/libvpx,iniwf/webm.libvpx,Laknot/libvpx,Distrotech/libvpx,reimaginemedia/webm.libvpx,lyx2014/libvpx_c,pcwalton/libvpx,kalli123/webm.libvpx,Laknot/libvpx,reimaginemedia/webm.libvpx,matanbs/vp982,lyx2014/libvpx_c,n4t/libvpx,turbulenz/libvpx,matanbs/webm.libvpx,Laknot/libvpx,jacklicn/webm.libvpx,altogother/webm.libvpx,jmvalin/aom,openpeer/libvpx_new,kalli123/webm.libvpx,charup/https---github.com-webmproject-libvpx-,Maria1099/webm.libvpx,lyx2014/libvpx_c,Laknot/libvpx,reimaginemedia/webm.libvpx,running770/libvpx,shacklettbp/aom,WebRTC-Labs/libvpx,goodleixiao/vpx,mwgoldsmith/vpx,reimaginemedia/webm.libvpx,Suvarna1488/webm.libvpx,Distrotech/libvpx,kim42083/webm.libvpx,ittiamvpx/libvpx,n4t/libvpx,Distrotech/libvpx,zofuthan/libvpx,vasilvv/esvp8,jmvalin/aom,turbulenz/libvpx,turbulenz/libvpx,matanbs/vp982,shyamalschandra/libvpx,kim42083/webm.libvpx,ittiamvpx/libvpx-1,goodleixiao/vpx,abwiz0086/webm.libvpx,kalli123/webm.libvpx,Acidburn0zzz/webm.libvpx,Suvarna1488/webm.libvpx,openpeer/libvpx_new,Acidburn0zzz/webm.libvpx,hsueceumd/test_hui,sanyaade-teachings/libvpx,liqianggao/libvpx,running770/libvpx,mwgoldsmith/libvpx,iniwf/webm.libvpx,lyx2014/libvpx_c,vasilvv/esvp8,pcwalton/libvpx,VTCSecureLLC/libvpx,webmproject/li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