Fix examples/Makefile jemalloc error

Summary: compile and link with jemalloc in examples binaries

Test Plan:
cd examples
make -j64

Reviewers: andrewkr, sdong

Reviewed By: sdong

Subscribers: andrewkr, dhruba, yoshinorim

Differential Revision: https://reviews.facebook.net/D59457

examples/Makefile

@@ -1,5 +1,13 @@
 include ../make_config.mk
 
+ifndef DISABLE_JEMALLOC
+	ifdef JEMALLOC
+		PLATFORM_CXXFLAGS += "-DROCKSDB_JEMALLOC"
+	endif
+	EXEC_LDFLAGS := $(JEMALLOC_LIB) $(EXEC_LDFLAGS) -lpthread
+	PLATFORM_CXXFLAGS += $(JEMALLOC_INCLUDE)
+endif
+
 .PHONY: clean librocksdb
 
 all: simple_example column_families_example compact_files_example c_simple_example optimistic_transaction_example transaction_example