How can I compile dlib external dependency zlib with -fPIC flag?

[posutsai]

I am using dlib with pybind11 to build a python extension and compiler is gcc in c++11. When I try to compile my code it always shows following error message, I think it may be that I didn't add -fPIC flag in zlib compilation.

//usr/local/lib/libdlib.a(zutil.c.o): relocation R_X86_64_PC32 against symbol z_errmsg' can not be used when making a shared object; recompile with -fPIC

I try to compile the same code without pybind11 too. And it works perfectly. Following is my command in my Makefile.

pybind11 version:
g++ -O3 -Wall -shared -std=c++11 -fPIC pkg-config --cflags --libs glib-2.0 python3 -m pybind11 --includes $^ -lpthread -lX11 -ldlib -lglib-2.0 -lz /usr/local/lib/libz.a -l
jpeg -o wsi_readerpython3-config --extension-suffix

without pybind11 version:
g++ -O3 -std=c++11 pkg-config --cflags --libs glib-2.0 -I/usr/include/boost $^ -ldlib -ljpeg -lglib-2.0 -lpthread -o out

[posutsai]

I follow the solution in this issue and solve it already.
pybind/pybind11#466
I manually add set_target_properties(dlib PROPERTIES POSITION_INDEPENDENT_CODE TRUE)
before add_subdirectory in CMakeLists.txt.