During the bootstrap phase, when building the minimal llvm library on

PowerPC, add lib/Support/Atomic.cpp.  This is needed because upstream
llvm revision r271821 disabled the use of std::call_once, which causes
some fallback functions from Atomic.cpp to be used instead.

Reported by:	Mark Millard
PR:		214902
X-MFC-With:	309124

lib/clang/libllvmminimal/Makefile

@@ -7,6 +7,9 @@ INTERNALLIB=
 
 SRCDIR=		lib
 SRCS+=		Support/APInt.cpp
+.if ${MACHINE_ARCH:Mpowerpc*} != ""
+SRCS+=		Support/Atomic.cpp
+.endif
 SRCS+=		Support/CommandLine.cpp
 SRCS+=		Support/ConvertUTF.c
 SRCS+=		Support/ConvertUTFWrapper.cpp