difference with long datatype in 64bit gcc and msvc++

[Kevin Koltzau]

gcc and msvc++ have different opinions on the size of a long in 64bit code, 
gcc has sizeof(long)==8 while msvc++ has sizeof(long)==4

Binary compatibility with win64 will be just about impossible as the long 
datatype is used extensively throughout the headers and code

doing -Dlong=int works in simple cases, but not as a general rule

I'm at a loss as to where to go from here, suggestions are most welcome.