Install wasm libraries in `INSTALL/lib` directory.

The default detected libdir is based on the build architecture.
On ubuntu, it is `lib/x86_64-linux-gnu` which is obviously not the right
directory.

Let's simply use `lib`.

Fix #556

kiwixbuild/platforms/wasm.py

@@ -9,6 +9,7 @@ class WasmPlatformInfo(PlatformInfo):
     static = True
     build = 'wasm'
     arch_full = 'wasm64-emscripten'
+    libdir = "lib"
     #arch_full = 'wasm64-linux'
     toolchain_names = ['emsdk']
     compatible_hosts = ['fedora', 'debian']