Fix generic build on Max OS X 10.7 Lion

    Recover variable build_mac_version which is removed on
    commit 644dc16 and added on commit 9ce06f1.

    Without this, ranlib libSDL.a is executed on Lion which
    causes build fail of emulator-arm.

Change-Id: I06144a288921f8f968ef457999398c1b9152d4aa
diff --git a/core/combo/HOST_darwin-x86.mk b/core/combo/HOST_darwin-x86.mk
index 5ab2c0d..8be6a42 100644
--- a/core/combo/HOST_darwin-x86.mk
+++ b/core/combo/HOST_darwin-x86.mk
@@ -23,6 +23,7 @@
 HOST_GLOBAL_CFLAGS += -m32
 HOST_GLOBAL_LDFLAGS += -m32
 
+build_mac_version := $(shell sw_vers -productVersion)
 mac_sdk_version := 10.6
 mac_sdk_root := /Developer/SDKs/MacOSX$(mac_sdk_version).sdk
 ifeq ($(wildcard $(mac_sdk_root)),)