Automatically set LITE=1 on passing OPT="-DROCKSDB_LITE" (facebook#4671)

Summary:
In facebook#4652 we are setting -Os for lite builds only when LITE=1 is specified. But currently almost all the users invoke lite build via OPT="-DROCKSDB_LITE=1". So this diff tries to set LITE=1 when users already pass in -DROCKSDB_LITE=1 via the command line.
Pull Request resolved: facebook#4671

Differential Revision: D13033801

Pulled By: sagar0

fbshipit-source-id: e7b506cee574f9e3f42221ee6647915011c78d78

Makefile

@@ -95,9 +95,17 @@ endif
 
 # Lite build flag.
 LITE ?= 0
-ifneq ($(LITE), 0)
+ifeq ($(LITE), 0)
+ifneq ($(filter -DROCKSDB_LITE,$(OPT)),)
+  # Be backward compatible and support older format where OPT=-DROCKSDB_LITE is
+  # specified instead of LITE=1 on the command line.
+  LITE=1
+endif
+else ifeq ($(LITE), 1)
+ifeq ($(filter -DROCKSDB_LITE,$(OPT)),)
 	OPT += -DROCKSDB_LITE
 endif
+endif
 
 # Figure out optimize level.
 ifneq ($(DEBUG_LEVEL), 2)