Get the architecture from ld rather than uname on OS X.

src/build/Common.gmake

@@ -196,8 +196,13 @@ ifndef os
 endif
 os      :=	$(shell echo $(os) | tr '[A-Z]' '[a-z]' | tr ' ' '_')
 
-machine		:=	$(shell if uname -m | egrep -v "(i[3456789]*|x)86" > /dev/null; then uname -m | tr "[A-Z]" "[a-z]" | tr " " "_" ; fi)
-machine		:=	$(shell if uname -m | egrep "64" > /dev/null; then uname -m | tr "[A-Z]" "[a-z]" | tr " " "_" ; else echo $(machine) ; fi)
+ifeq ($(os),darwin)
+ machine		:=	$(shell ld -w 2>&1 | sed -E 's/.*[[:space:]]//')
+else
+ machine		:=	$(shell if uname -m | egrep -v "(i[3456789]*|x)86" > /dev/null; then uname -m | tr "[A-Z]" "[a-z]" | tr " " "_" ; fi)
+ machine		:=	$(shell if uname -m | egrep "64" > /dev/null; then uname -m | tr "[A-Z]" "[a-z]" | tr " " "_" ; else echo $(machine) ; fi)
+endif
+
 ifeq ($(machine),x86_64)
  machine	:= x64
 endif