moc mangles some function names

When building a Qt application on i686, moc causes:

moc_iconapplet_FERWDM656PUOUJ.cpp:128:21: error: 'class IconApplet' has no member named 'open64'; did you mean 'open'?

This is due to moc not defining _GNUC_ >= 2, so it emits code that does not match the header.

To reproduce, just run

moc -I/usr/include -D_FILE_OFFSET_BITS=64 <attachment> | grep open64

on a i686 system with glibc.

It works with

moc -I/usr/include -D _GNUC_=6 -D_FILE_OFFSET_BITS=64 <attachment> | grep open64