Webassembly Kit fails to auto-detect properly, blocks manual entry

Related to QTCREATORBUG-23126

The Webassembly kit fails to autodetect a 'standard' emscripten install.  It also disables the "Choose" button and doesn't allow editing the compiler path, making the compiler (and thus kit) unusable.

Activating the emsdk (./emsdk activate) on a toolchain creates the .emscripten file in the emsdk install directory, but auto-detect checks the ~/. location.  To work around this, after activation the .emscripten file can be copied to ~/. where it will be found by auto-detect.

Unfortunately the file is parsed incorrectly.  While the individual defines are recognized, the emsdk_path string substitution doesn't occur, so the compiler location is prepended with "+ emsdk_path + "  instead of the actual location.

Manually editing each of the defines in ~/.emscripten with the emsdk path (LLVM_ROOT = '/Users/tec/emsdk/fastcomp-clang/e1.38.27_64bit/binaryen', etc)  will result in the compiler detecting properly, and in turn it can now be selected as the compiler to get the kit working.