Step 1: Clone source code from git repos

git clone https://android.googlesource.com/platform/system/core.git

Step 2: Write a standalone Makefile

vim core/fastboot/Makefile

# Makefile for fastboot

SRCS+=protocol.c
SRCS+=engine.c
SRCS+=bootimg.c
SRCS+=fastboot.c
SRCS+=usb_linux.c
SRCS+=util_linux.c

VPATH+= ../libzipfile
SRCS+= centraldir.c
SRCS+= zipfile.c
 
CPPFLAGS+= -DADB_HOST=1
CPPFLAGS+= -DHAVE_FORKEXEC=1
CPPFLAGS+= -DHAVE_SYMLINKS
CPPFLAGS+= -DHAVE_TERMIO_H
CPPFLAGS+= -D_GNU_SOURCE
CPPFLAGS+= -D_XOPEN_SOURCE
CPPFLAGS+= -I.
CPPFLAGS+= -I../include
CPPFLAGS+= -I../mkbootimg
CPPFLAGS+= -I../../../external/zlib
 
CFLAGS+= -O2 -Wno-unused-parameter
LDFLAGS= 
LIBS= -lrt -lpthread -lz
 
TOOLCHAIN= mipsel-unknown-linux-gnu-
CC= $(TOOLCHAIN)gcc
LD= $(TOOLCHAIN)gcc
 
OBJS= $(SRCS:.c=.o)
 
all: fastboot
 
fastboot: $(OBJS)
	$(LD) -o $@ $(LDFLAGS) $(OBJS) $(LIBS)
 
clean:
	rm -rf $(OBJS)

Step 3: Build

cd core/fastboot
make

Over!