QT5.7有自带虚拟键盘，在QT5.6下要单独编译。
QT5.6下的官方虚拟键盘源码
在将QT5.6添加支持QML后，就可以添加虚拟键盘的支持
在编译过程中会出现警告
note: the mangling of ‘va_list’ has changed in GCC 4.4
解决办法：
I think that the warning is accurate; the mangling of va_list has
indeed changed on ARM in GCC 4.4 in order to conform to the ARM ABI
specifications. There is an option to turn off warnings about PSABI
issues; -Wno-psabi. I think that option (if not some stronger
option) should be used.
其出处为https://gcc.gnu.org/bugzilla/show_bug.cgi?id=42748