configure: enable PIC for shared libs by default
configure: enable PIC for shared libs by default

Shared libs generally require PIC, so this saves a little typing at
configure time.

Change-Id: I357d70cc68434f3283fee78873052d2b7d77c777

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vpx,lyx2014/libvpx_c,genesi/libvpx0,turbulenz/libvpx,openpeer/libvpx_new,Laknot/libvpx,turbulenz/libvpx,smarter/aom,hsueceumd/test_hui,n4t/libvpx,charup/https---github.com-webmproject-libvpx-,lyx2014/libvpx_c,abwiz0086/webm.libvpx,lyx2014/libvpx_c,kim42083/webm.libvpx,mwgoldsmith/libvpx,Maria1099/webm.libvpx,Laknot/libvpx,altogother/webm.libvpx,mwgoldsmith/vpx,jmvalin/aom,Laknot/libvpx,stewnorriss/libvpx,Maria1099/webm.libvpx,Topopiccione/libvpx,luctrudeau/aom,awatry/libvpx.opencl,liqianggao/libvpx,kleopatra999/webm.libvpx,ittiamvpx/libvpx,GrokImageCompression/aom,openpeer/libvpx_new,openpeer/libvpx_new,felipebetancur/libvpx,ShiftMediaProject/libvpx,thdav/aom,iniwf/webm.libvpx,turbulenz/libvpx,ShiftMediaProject/libvpx,pcwalton/libvpx,rikaunite/gst-opera_libvpx,running770/libvpx,genesi/libvpx0,n4t/libvpx,genesi/libvpx0,shareefalis/libvpx,ittiamvpx/libvpx-1,Laknot/libvpx,mwgoldsmith/libvpx,luctrudeau/aom,kleopatra999/webm.libvpx,webmproject/libvpx,mbebenita/aom,Suvarna1488/webm.libvpx,enmasse-entertainment/libvpx,shacklettbp/aom,webmproject/libvpx,smarter/aom,rikaunite/gst-opera_libvpx,kleopatra999/webm.libvpx,vasilvv/esvp8,altogother/webm.libvpx,Distrotech/libvpx,WebRTC-Labs/libvpx,jdm/libvpx,hsueceumd/test_hui,stewnorriss/libvpx,liqianggao/libvpx,shyamalschandra/libvpx,shacklettbp/aom,matanbs/vp982,shacklettbp/aom,shareefalis/libvpx,goodleixiao/vpx