how to fix 'undefined reference to `main' collect2: error: ld returned 1 exit status' - c

Question

When I am trying to compile the host code using make command. It gave me this error:
`/usr/lib/gcc/x86_64-redhat-linux/4.8.5/../../../../lib64/crt1.o: In function `_start':
(.text+0x20): undefined reference to `main'
collect2: error: ld returned 1 exit status
make: *** [bin/host] Error 1
`
Makefile:
ifeq ($(VERBOSE),1)
ECHO :=
else
ECHO := #
endif
# Where is the Intel(R) FPGA SDK for OpenCL(TM) software?
ifeq ($(wildcard $(INTELFPGAOCLSDKROOT)),)
$(error Set INTELFPGAOCLSDKROOT to the root directory of the Intel(R) FPGA SDK for OpenCL(TM) software installation)
endif
ifeq ($(wildcard $(INTELFPGAOCLSDKROOT)/host/include/CL/opencl.h),)
$(error Set INTELFPGAOCLSDKROOT to the root directory of the Intel(R) FPGA SDK for OpenCL(TM) software installation.)
endif
# OpenCL compile and link flags.
AOCL_COMPILE_CONFIG := $(shell aocl compile-config )
AOCL_LINK_CONFIG := $(shell aocl link-config )
# Compilation flags
ifeq ($(DEBUG),1)
CXXFLAGS += -g
else
CXXFLAGS += -O2
endif
# Compiler
CXX := g++
# Target
TARGET := host
TARGET_DIR := bin
# Directories
INC_DIRS := ../common/inc
LIB_DIRS :=
# Files
INCS := $(wildcard )
SRCS := $(wildcard host/src/*.cpp ../common/src/AOCLUtils/*.cpp)
LIBS := rt pthread
# Make it all!
all : $(TARGET_DIR)/$(TARGET)
# Host executable target.
$(TARGET_DIR)/$(TARGET) : Makefile $(SRCS) $(INCS) $(TARGET_DIR)
$(ECHO)$(CXX) $(CPPFLAGS) $(CXXFLAGS) -fPIC $(foreach D,$(INC_DIRS),-I$D) \
$(AOCL_COMPILE_CONFIG) $(SRCS) $(AOCL_LINK_CONFIG) \
$(foreach D,$(LIB_DIRS),-L$D) \
$(foreach L,$(LIBS),-l$L) \
-o $(TARGET_DIR)/$(TARGET)
$(TARGET_DIR) :
$(ECHO)mkdir $(TARGET_DIR)
# Standard make targets
clean :
$(ECHO)rm -f $(TARGET_DIR)/$(TARGET)
.PHONY : all clean