win: version from os name(winxp,win7 etc.)

update nvenc patch to be compatible with master branch

win: update shortcuts. skip ci

ci: xcode11, clang-9

update patches to compatible with ffmpeg master and 4.2

README: add vs2019. skip ci

android: explicitly set --cc if use gcc

restore IS_CLANG for multi arch config

ci: add vs2019

libffmpeg: add objects in compat

libffmpeg: with version, install, def create by make

libffmpeg: fix xargs error on appveyor

libffmpeg: process link script, required by macOS

build a single ffmpeg dynamic library

add vs2019 shortcuts