We need macOS 10.9 for std::atomic

src/build/Common.gmake

@@ -371,7 +371,7 @@ ifeq ($(os),haiku)
  CFLAGS	+=	-D__unix__ -DNEEDS_FORKPTY
 endif
 ifeq ($(os),darwin)
- MIN_MAC_OSX_VERSION ?= 10.7
+ MIN_MAC_OSX_VERSION ?= 10.9
  CFLAGS +=  -D__unix__ -fno-common -D__DARWIN__
  CFLAGS +=  -mmacosx-version-min=$(MIN_MAC_OSX_VERSION)
  LDFLAGS += -mmacosx-version-min=$(MIN_MAC_OSX_VERSION)