At least starting with ca83115b
the source code cannot be compiled with anything older than GCC 4.8.5.

Furthermore, 64-bit atomic read-modify-write operations on IA-32
would depend on the LOCK CMPXCHG8B instruction, which was introduced
in the Intel Pentium. Our IA-32 builds ought to be -march=i686
starting with commit 9cabc9fd.

Approved by Sergei Golubchik