Fix compiling Mac OS 10.5 Universal App Bundle

Need to be able to specify minimum Mac OS X version outside of the
Makefile to avoid conflicting CFLAGS.
Moved -mmacosx-version-min LDFLAGS into the Makefile.
Moved -arch x86_64 from OPTIMIZEVM to CFLAGS to fix linker errors
(previously make-macosx-ub.sh passed it to CFLAGS manually).

Makefile

@@ -409,7 +409,17 @@ ifeq ($(PLATFORM),darwin)
   RENDERER_LIBS=
   OPTIMIZEVM=
 
-  BASE_CFLAGS += -mmacosx-version-min=10.7 -DMAC_OS_X_VERSION_MIN_REQUIRED=1070
+  # Default minimum Mac OS X version
+  ifeq ($(MACOSX_VERSION_MIN),)
+    MACOSX_VERSION_MIN=10.7
+  endif
+
+  # Multiply by 100 and then remove decimal. 10.7 -> 1070.0 -> 1070
+  MAC_OS_X_VERSION_MIN_REQUIRED=$(shell echo '$(MACOSX_VERSION_MIN) * 100' | bc | cut -d. -f1)
+
+  LDFLAGS += -mmacosx-version-min=$(MACOSX_VERSION_MIN)
+  BASE_CFLAGS += -mmacosx-version-min=$(MACOSX_VERSION_MIN) \
+                 -DMAC_OS_X_VERSION_MIN_REQUIRED=$(MAC_OS_X_VERSION_MIN_REQUIRED)
 
   ifeq ($(ARCH),ppc)
     BASE_CFLAGS += -arch ppc -faltivec
@@ -425,7 +435,8 @@ ifeq ($(PLATFORM),darwin)
     BASE_CFLAGS += -arch i386 -m32 -mstackrealign
   endif
   ifeq ($(ARCH),x86_64)
-    OPTIMIZEVM += -arch x86_64 -mfpmath=sse
+    OPTIMIZEVM += -mfpmath=sse
+    BASE_CFLAGS += -arch x86_64
   endif
 
   # When compiling on OSX for OSX, we're not cross compiling as far as the