configure.ac : Tweak for x32 architecture.

The x32 architecture uses and ILP32 (32 bit ints, longs and pointers)
on an x86_64 CPU. Since the CPU is x86_64 we need to set FLAC__CPU_X86_64
even though the pointer size is 32 bits.

Patch-from: Stuart Shelton
Closes: https://sourceforge.net/p/flac/bugs/427/
1 file changed