Docker image not cached lto libraries

```
$ emcc astyle/*.cpp --no-entry -flto=full -DASTYLE_LIB -DNDEBUG=1 -std=c++11 -O3 -o dist/astyle.wasm
cache:INFO: generating system asset: crt1_reactor.o... (this will be cached in "/emsdk/upstream/emscripten/cache/wasm-lto/crt1_reactor.o" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libc.a... (this will be cached in "/emsdk/upstream/emscripten/cache/wasm-lto/libc.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libcompiler_rt.a... (this will be cached in "/emsdk/upstream/emscripten/cache/wasm-lto/libcompiler_rt.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libc++-noexcept.a... (this will be cached in "/emsdk/upstream/emscripten/cache/wasm-lto/libc++-noexcept.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libc++abi-noexcept.a... (this will be cached in "/emsdk/upstream/emscripten/cache/wasm-lto/libc++abi-noexcept.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libdlmalloc.a... (this will be cached in "/emsdk/upstream/emscripten/cache/wasm-lto/libdlmalloc.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libpthread_stub.a... (this will be cached in "/emsdk/upstream/emscripten/cache/wasm-lto/libpthread_stub.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libstandalonewasm.a... (this will be cached in "/emsdk/upstream/emscripten/cache/wasm-lto/libstandalonewasm.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libc_rt_wasm.a... (this will be cached in "/emsdk/upstream/emscripten/cache/wasm-lto/libc_rt_wasm.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libsockets.a... (this will be cached in "/emsdk/upstream/emscripten/cache/wasm-lto/libsockets.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system asset: generated_struct_info.json... (this will be cached in "/emsdk/upstream/emscripten/cache/wasm-lto/generated_struct_info.json" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system asset: crt1_reactor.o... (this will be cached in "/emsdk/upstream/emscripten/cache/wasm-lto/crt1_reactor.o" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libc.a... (this will be cached in "/emsdk/upstream/emscripten/cache/wasm-lto/libc.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libcompiler_rt.a... (this will be cached in "/emsdk/upstream/emscripten/cache/wasm-lto/libcompiler_rt.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libc++-noexcept.a... (this will be cached in "/emsdk/upstream/emscripten/cache/wasm-lto/libc++-noexcept.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libc++abi-noexcept.a... (this will be cached in "/emsdk/upstream/emscripten/cache/wasm-lto/libc++abi-noexcept.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libdlmalloc.a... (this will be cached in "/emsdk/upstream/emscripten/cache/wasm-lto/libdlmalloc.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libpthread_stub.a... (this will be cached in "/emsdk/upstream/emscripten/cache/wasm-lto/libpthread_stub.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libstandalonewasm.a... (this will be cached in "/emsdk/upstream/emscripten/cache/wasm-lto/libstandalonewasm.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libc_rt_wasm.a... (this will be cached in "/emsdk/upstream/emscripten/cache/wasm-lto/libc_rt_wasm.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system library: libsockets.a... (this will be cached in "/emsdk/upstream/emscripten/cache/wasm-lto/libsockets.a" for subsequent builds)
cache:INFO: - ok
cache:INFO: generating system asset: generated_struct_info.json... (this will be cached in "/emsdk/upstream/emscripten/cache/wasm-lto/generated_struct_info.json" for subsequent builds)
cache:INFO: - ok
```