User should not change between emcc install and use

src/ci/docker/asmjs/Dockerfile

@@ -24,13 +24,15 @@ ENV PATH=$PATH:/emsdk-portable
 ENV PATH=$PATH:/emsdk-portable/upstream/emscripten/
 ENV PATH=$PATH:/emsdk-portable/node/12.9.1_64bit/bin/
 ENV BINARYEN_ROOT=/emsdk-portable/upstream/
-ENV EM_CONFIG=/emsdk-portable/.emscripten
 
 ENV TARGETS=asmjs-unknown-emscripten
 
 # Use -O1 optimizations in the link step to reduce time spent optimizing JS.
 ENV EMCC_CFLAGS=-O1
 
+# Emscripten installation is user-specific
+ENV NO_CHANGE_USER=1
+
 ENV SCRIPT python2.7 ../x.py test --target $TARGETS
 
 # This is almost identical to the wasm32-unknown-emscripten target, so

src/ci/docker/scripts/emscripten.sh

@@ -21,13 +21,3 @@ git clone https://github.com/emscripten-core/emsdk.git /emsdk-portable
 cd /emsdk-portable
 hide_output ./emsdk install 1.38.46-upstream
 ./emsdk activate 1.38.46-upstream
-
-# Compile and cache libc
-source ./emsdk_env.sh
-echo "main(){}" > a.c
-HOME=/emsdk-portable/ emcc a.c
-rm -f a.*
-
-# Make emsdk usable by any user
-cp /root/.emscripten /emsdk-portable
-chmod a+rxw -R /emsdk-portable

src/ci/docker/wasm32/Dockerfile

@@ -24,13 +24,15 @@ ENV PATH=$PATH:/emsdk-portable
 ENV PATH=$PATH:/emsdk-portable/upstream/emscripten/
 ENV PATH=$PATH:/emsdk-portable/node/12.9.1_64bit/bin/
 ENV BINARYEN_ROOT=/emsdk-portable/upstream/
-ENV EM_CONFIG=/emsdk-portable/.emscripten
 
 ENV TARGETS=wasm32-unknown-emscripten
 
 # Use -O1 optimizations in the link step to reduce time spent optimizing.
 ENV EMCC_CFLAGS=-O1
 
+# Emscripten installation is user-specific
+ENV NO_CHANGE_USER=1
+
 # FIXME: Re-enable these tests once https://github.com/rust-lang/cargo/pull/7476
 # is picked up by CI
 ENV SCRIPT python2.7 ../x.py test --target $TARGETS \