Compilation on Windows 32 bit not working

[ofajardo]

Windows compilation fails for 32 bit:

windows: build\temp.win32-3.8\Release\pyreadr\libs\librdata\src\rdata_write.o:rdata_write.c:(.text+0x67a): undefined reference to `_mkgmtime32'

For now, raise an exception in setup.py if trying to compile for 32 bit, so that people using pip don't get the above exception but a nice message saying, please use 64 bit

[ofajardo]

Seems to be a bug in MingW Exiv2/exiv2#473