makefile.unix: add support for building vwebp
makefile.unix: add support for building vwebp

standalone from the normal examples due to the additional OpenGL
dependencies.
$ make -f makefile.unix examples/vwebp

Change-Id: I7e3f0b5e0328230cb32acdd1e2a011cbbb80e55d

yohunl/libwebp,ya7lelkom/libwebp,rxl194/libwebp,Aexyn/libwebp,Tekserve/libwebp,kalli123/webm.libwebp,reimaginemedia/webm.libwebp,Aexyn/libwebp,matanbs/webm.libwebp,Distrotech/libwebp,keane83/BLE_IM,Suvarna1488/webm.libwebp,zofuthan/libwebp,altogother/webm.libwebp,PKRoma/libwebp,imazen/libwebp,Acidburn0zzz/webm.libwebp,comoyo/gonzo-libwebp,altogother/webm.libwebp,kim42083/webm.libwebp,ericmckean/webm.libwebp,Tekserve/libwebp,rxl194/libwebp,kalli123/webm.libwebp,webmproject/libwebp,Maria1099/webm.libwebp,ericmckean/webm.libwebp,appunite/libwebp,ttyangf/libwebp,redengineer/libwebp,yohunl/libwebp,ttyangf/libwebp,dumganhar/libwebp,kalli123/webm.libwebp,kleopatra999/webm.libwebp,ya7lelkom/libwebp,gshORTON/webm.libwebp,abwiz0086/webm.libwebp,keane83/BLE_IM,iniwf/webm.libwebp,PKRoma/libwebp,kim42083/webm.libwebp,altogother/webm.libwebp,appunite/libwebp,cysp/libwebp,ya7lelkom/libwebp,appunite/libwebp,Tekserve/libwebp,Acidburn0zzz/webm.libwebp,Tekserve/libwebp,Distrotech/libwebp,Distrotech/libwebp,yohunl/libwebp,iniwf/webm.libwebp,imazen/libwebp,jacklicn/libwebp,webmproject/libwebp,rxl194/libwebp,keane83/BLE_IM,jacklicn/libwebp,jacklicn/libwebp,kleopatra999/webm.libwebp,gshORTON/webm.libwebp,redengineer/libwebp,redengineer/libwebp,Acidburn0zzz/webm.libwebp,matanbs/webm.libwebp,comoyo/gonzo-libwebp,kleopatra999/webm.libwebp,jacklicn/libwebp,cysp/libwebp,ya7lelkom/libwebp,appunite/libwebp,imazen/libwebp,cysp/libwebp,yohunl/libwebp,imazen/libwebp,ericmckean/webm.libwebp,comoyo/gonzo-libwebp,jiehu5114/libwebp,reimaginemedia/webm.libwebp,abwiz0086/webm.libwebp,reimaginemedia/webm.libwebp,iniwf/webm.libwebp,dumganhar/libwebp,webmproject/libwebp,abwiz0086/webm.libwebp,Suvarna1488/webm.libwebp,imazen/libwebp,zofuthan/libwebp,kalli123/webm.libwebp,iniwf/webm.libwebp,matanbs/webm.libwebp,webmproject/libwebp,PKRoma/libwebp,PKRoma/libwebp,gshORTON/webm.libwebp,altogother/webm.libwebp,yohunl/libwebp,gshORTON/webm.libwebp,Maria1099/webm.libwebp,Acidburn0zzz/webm.libwebp,kim42083/webm.libwebp,zofuthan/libwebp,comoyo/gonzo-libwebp,zofuthan/libwebp,comoyo/gonzo-libwebp,ttyangf/libwebp,kim42083/webm.libwebp,ericmckean/webm.libwebp,appunite/libwebp,matanbs/webm.libwebp,kalli123/webm.libwebp,zofuthan/libwebp,kleopatra999/webm.libwebp,reimaginemedia/webm.libwebp,matanbs/webm.libwebp,iniwf/webm.libwebp,keane83/BLE_IM,redengineer/libwebp,PKRoma/libwebp,webmproject/libwebp,jiehu5114/libwebp,PKRoma/libwebp,abwiz0086/webm.libwebp,gshORTON/webm.libwebp,kleopatra999/webm.libwebp,keane83/BLE_IM,abwiz0086/webm.libwebp,Maria1099/webm.libwebp,dumganhar/libwebp,Suvarna1488/webm.libwebp,rxl194/libwebp,Aexyn/libwebp,Aexyn/libwebp,Acidburn0zzz/webm.libwebp,Suvarna1488/webm.libwebp,ttyangf/libwebp,appunite/libwebp,comoyo/gonzo-libwebp,reimaginemedia/webm.libwebp,altogother/webm.libwebp,jiehu5114/libwebp,jiehu5114/libwebp,Maria1099/webm.libwebp,cysp/libwebp,kim42083/webm.libwebp,jiehu5114/libwebp,Suvarna1488/webm.libwebp,redengineer/libwebp,ttyangf/libwebp,ericmckean/webm.libwebp,Aexyn/libwebp,rxl194/libwebp,ya7lelkom/libwebp,comoyo/gonzo-libwebp,Maria1099/webm.libwebp,jacklicn/libwebp