I have the same problem with Qt 5.8 and MinGW64 6.3:

C:/Program Files/mingw-w64/x86_64-6.3.0-posix-seh-rt_v5-rev1/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/6.3.0/../../../../x86_64-w64-mingw32/bin/as.exe: .obj\debug\IFCReaderGen1.o: too many sections (40453)
{standard input}: Assembler messages:
{standard input}: Fatal error: can't write 169 bytes to section .text of .obj\debug\IFCReaderGen1.o because: 'File too big'

~/> as.exe --version
GNU assembler (GNU Binutils) 2.27
This assembler was configured for a target of `x86_64-w64-mingw32'.