extras: add wasm-emscripten build script

- merge the previous build scripts into one
- allow building outside of vlc source
- add wasm32-emscripten ci
19 jobs for !20 with upstream/vlc.js.2 in 211 minutes (queued for 4 seconds)
latest detached
Status Job ID Name Coverage
  Build
passed #623333
amd64 docker
android-arm

00:10:39

passed #623334
amd64 docker
android-arm64

00:08:53

passed #623335
amd64 docker
android-x86

00:09:57

passed #623336
amd64 docker
android-x86_64

00:09:08

passed #623324
amd64 docker
debian

00:25:14

passed #623329
catalina amd64
ios-arm64

00:17:50

passed #623330
catalina amd64
ios-armv7

00:20:34

passed #623331
catalina amd64
ios-simulator-x86_64

00:24:35

passed #623328
catalina amd64
macos-arm64

00:33:10

passed #623327
catalina amd64
macos-x86_64

00:46:51

passed #623326
amd64 docker
raspbian-arm

00:11:00

passed #623325
amd64 docker
snap

00:39:30

passed #623332
catalina amd64
tvos-arm64

00:20:41

passed #623323
amd64 docker
uwp-arm64-libvlc-llvm

00:13:56

passed #623322
amd64 docker
uwp64-libvlc-llvm

00:14:40

passed #623337
wasm32-emscripten-build
wasm32-emscripten-build

00:05:01

passed #623319
amd64 docker
win32

00:35:22

passed #623320
amd64 docker
win64

00:21:13

passed #623321
amd64 docker
win64-llvm

00:20:39