devel/build2: Fix build on i386

The powerpc build progresses much further with the same flag set, but now
segfaults when the do-install target is run.

> Staging for build2-0.16.0

> Generating temporary packing list

Invalid data memory access: 0xf2e018b8
Invalid data memory access: 0x81390500
Invalid data memory access: 0x00000048

• Signal 11

Approved by: portmgr (blanket)