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)

devel/build2/Makefile

@@ -11,11 +11,14 @@ WWW=		https://build2.org
 LICENSE=	BSD2CLAUSE BSD3CLAUSE MIT
 LICENSE_COMB=	multi
 
-BROKEN_i386=	error: timestamp is not lock-free on this architecture
-BROKEN_powerpc=	error: timestamp is not lock-free on this architecture
+BROKEN_powerpc=	fails in stage: Invalid data memory access
 
 USES=		gmake pkgconfig sqlite tar:xz
 
+# Fix build on i386/powerpc: error: timestamp is not lock-free on this architecture
+CXXFLAGS_i386=		-DLIBBUILD2_ATOMIC_NON_LOCK_FREE
+CXXFLAGS_powerpc=	-DLIBBUILD2_ATOMIC_NON_LOCK_FREE
+
 # warning: clang@/usr/local/libexec/ccache/clang looks like a ccache wrapper
 #  info: ccache cannot be used as a C compiler
 #  info: use config.c to override