add cmake configuration summary
add cmake configuration summary

This commit adds the message command to CMakeLists.txt to output a
summary of some useful information. The following will be displayed when
with this addition:
$ cd build && cmake ..
-- summary of build options:

    Install prefix:  /usr/local
    Target system:   Darwin
    Compiler:
      C compiler:    /work/ccache/ccache
      CFLAGS:         -g -I/work/nodejs/libuv-build/include
    Libuv version:   1.32.0
    Libuv lib:       /work/wasm/uvwasi/build/_deps/libuv-build

-- Configuring done
-- Generating done
-- Build files have been written to: //work/wasm/uvwasi/build

nodejs/uvwasi