Emscripten wasm side module library

[danoli3]

As Emscripten libraries require executable code rather than static this fixes issues for WASM using side module. .wasm extension target

Can be interpreted as .a with this executable byte code

This can be used for patching your own libpng frameworks. Emscripten comes with a em port however versions are not always up to date with latest changes so this is convenient for cmake / developers / frameworks.

I think also we can assume libpng is being compiled by Emscripten via emmake

Example Cmake commands:

mkdir -p build_$TYPE
        cd build_$TYPE
        rm -f CMakeCache.txt *.a *.o *.wasm

        ZLIB_ROOT="$LIBS_ROOT/zlib/"
        ZLIB_INCLUDE_DIR="$LIBS_ROOT/zlib/include"
        ZLIB_LIBRARY="$LIBS_ROOT/zlib/lib/$TYPE/zlib.wasm"

        $EMSDK/upstream/emscripten/emcmake cmake .. \
            ${DEFS} \
            -DCMAKE_TOOLCHAIN_FILE=$EMSDK/upstream/emscripten/cmake/Modules/Platform/Emscripten.cmake \
            -DCMAKE_C_STANDARD=17 \
            -DEMSCRIPTEN=ON \
            -DCMAKE_CXX_STANDARD=17 \
            -DCMAKE_CXX_STANDARD_REQUIRED=ON \
            -DCMAKE_CXX_FLAGS="-DUSE_PTHREADS=1 -std=c++17 -Wno-implicit-function-declaration -frtti -fPIC ${FLAG_RELEASE}" \
            -DCMAKE_C_FLAGS="-DUSE_PTHREADS=1 -std=c17 -Wno-implicit-function-declaration -frtti -fPIC ${FLAG_RELEASE}" \
            -DCMAKE_CXX_EXTENSIONS=OFF \
            -DCMAKE_INSTALL_PREFIX=Release \
            -DZLIB_ROOT=${ZLIB_ROOT} \
            -DZLIB_LIBRARY=${ZLIB_LIBRARY} \
            -DZLIB_INCLUDE_DIR=${ZLIB_INCLUDE_DIR} \
            -DZLIB_INCLUDE_DIRS=${ZLIB_INCLUDE_DIR} \
            -DCMAKE_BUILD_TYPE=Release \
            -DBUILD_SHARED_LIBS=ON \
            -DPNG_EXECUTABLES=OFF \
            -DPNG_BUILD_ZLIB=OFF
        cmake --build . --target install --config Release
        cd ..