browser-asmjs: Update to depend on existing image from "trzeci/emscripten"

This commit updates the "browser-asmjs" images to avoid systematic
rebuild of emscripten sdk. Instead, it introduces dependency on the
image maintained by @trzeci

Note also:

* emscripten sdk updated from 1.36.7 to 1.36.14

* symlinking of "/bin/bash" as "/bin/sh" is reverted. This ensures other
  images including file like "common.debian" and relying on standard "sh"
  behavior will work as expected.

* workaround associated with CMakeForceCompiler has been removed from
  Dockerfile. Emscripten as been fixed.
  See https://github.com/kripken/emscripten/pull/4477

* we will revisit once official images are available.
  See https://github.com/kripken/emscripten/issues/4682

browser-asmjs/Dockerfile.in

@@ -0,0 +1,45 @@
+FROM trzeci/emscripten:sdk-tag-1.36.14-64bit
+MAINTAINER Matt McCormick "matt.mccormick@kitware.com"
+
+# Revert back to "/bin/sh" as default shell
+# See https://github.com/asRIA/emscripten-docker/blob/master/Dockerfile.in#L4
+RUN rm /bin/sh && ln -s /bin/dash /bin/sh
+
+#include "common.debian"
+
+#include "common.docker"
+
+ENV EMSCRIPTEN_VERSION 1.36.14
+
+ENV PATH /emsdk_portable:/emsdk_portable/clang/tag-e${EMSCRIPTEN_VERSION}/build_tag-e${EMSCRIPTEN_VERSION}_64/bin:/emsdk_portable/emscripten/tag-${EMSCRIPTEN_VERSION}:${PATH}
+ENV CC=/emsdk_portable/emscripten/tag-${EMSCRIPTEN_VERSION}/emcc \
+  CXX=/emsdk_portable/emscripten/tag-${EMSCRIPTEN_VERSION}/em++ \
+  AR=/emsdk_portable/emscripten/tag-${EMSCRIPTEN_VERSION}/emar
+
+# Emscripten generates system libraries the firsts time it runs
+ADD test/ /tmp/test/
+RUN cd /tmp && \
+  /bin/echo -e "#include <iostream>\nint main() { std::cout << \"first run\"; return 0; }" > /tmp/first_run.cxx && \
+  $CXX /tmp/first_run.cxx -o a.out.js && \
+  rm /tmp/first_run.* && \
+  /bin/echo -e "#include <stdio.h>\nint main() { printf(\"first run\"); return 0; }" > /tmp/first_run.c && \
+  $CC /tmp/first_run.c -o a.out.js && \
+  rm /tmp/first_run.* a.out.js && \
+  cd /tmp/test && \
+  python /tmp/test/run.py; python /tmp/test/run.py && \
+  cd && rm -rf /tmp/test
+
+ENV DEFAULT_DOCKCROSS_IMAGE dockcross/browser-asmjs
+
+ENV CMAKE_TOOLCHAIN_FILE /emsdk_portable/emscripten/tag-${EMSCRIPTEN_VERSION}/cmake/Modules/Platform/Emscripten.cmake
+
+# Build-time metadata as defined at http://label-schema.org
+ARG BUILD_DATE
+ARG IMAGE
+ARG VCS_REF
+ARG VCS_URL
+LABEL org.label-schema.build-date=$BUILD_DATE \
+      org.label-schema.name=$IMAGE \
+      org.label-schema.vcs-ref=$VCS_REF \
+      org.label-schema.vcs-url=$VCS_URL \
+      org.label-schema.schema-version="1.0"