Use 'e' instead of 'i' constraints with 64-bit atomic operations on amd64.

The ADD, AND, OR, and SUB instructions take at most a 32-bit
sign-extended immediate operand. 64-bit constants that do not fit into
that constraint need to be loaded into a register. The 'i' constraint
tells the compiler it can pass any integer constant to the assembler,
whereas the 'e' constrain only permits constants that fit into a 32-bit
sign-extended value. This fixes using
atomic_add/clear/set/subtract_long/64 with constants that do not fit into
a 32-bit sign-extended immediate.

Reported by: several folks
Tested by: Pete Wright <pete@nomadlogic.org>
MFC after: 2 weeks