wasm: c++14 config.test fails on windows

Checking for C++14 support...
+ cd /d C:\Users\llorn\depot\qt\qt5\qt5-base\config.tests\c++14 && C:\Users\llorn\depot\qt\qt5\qt5-base\bin\qmake.exe "CONFIG -= qt debug_and_release app_bundle lib_bundle" "CONFIG += static warn_off console single_arch" -early "CONFIG += cross_compile" C:/Users/llorn/depot/qt/qt5/qt5-base/config.tests/c++14
+ cd /d C:\Users\llorn\depot\qt\qt5\qt5-base\config.tests\c++14 && set MAKEFLAGS=& mingw32-make
> em++ -c -s WASM_OBJECT_FILES=1 -O3 -std=gnu++1y -w -I. -I/.emscripten_ports/openssl/include -IC:\Users\llorn\depot\qt\qt5\qtbase\mkspecs\wasm-emscripten -o main.obj main.cpp
> sed -e s/@APPNAME@/c++14/g C:/Users/llorn/depot/qt/qt5/qtbase/mkspecs/features/wasm/../../../src/plugins/platforms/wasm/wasm_shell.html > C:/Users/llorn/depot/qt/qt5/qt5-base/config.tests/c++14/c++14.html
> copy /y C:\Users\llorn\depot\qt\qt5\qtbase\mkspecs\features\wasm\..\..\..\src\plugins\platforms\wasm\qtloader.js C:\Users\llorn\depot\qt\qt5\qt5-base\config.tests\c++14
> The syntax of the command is incorrect.
> mingw32-make: *** [Makefile:156: appjs] Error 1
test config.qtbase.tests.c++14 FAILED