[CMake] Linux 64 bit woes

[Robert Bielik]

I'm compiling under Ubuntu and want to generate 64 bit code. Is there a way to get cmake to generate
the correct settings in the Makefile ?

I tried adding -m64 (and -march=x86-64) but the __x86_64__ define does not seem to be set. I.e. when using
FD_SET it gets the #define from asm-i386/posix_types.h which then results in an assembler error:

Error: Incorrect register `%rax' used with `l' suffix

TIA
/R