[CMake] How to add -fPIC to a static library?

[Steve Lorimer]

I'm trying to create a static library with -fPIC specified.

add_library(cpp-netlib_pic
    STATIC
    ${SRCS})
set_property(TARGET cpp-netlib_pic PROPERTY POSITION_INDEPENDENT_CODE)

This doesn't work.

The library (cpp-netlib_pic) is built without the -fPIC flags.

Other targets which link against cpp-netlib_pic have -fPIC added to their
compiler flags, but the linking fails because cpp-netlib_pic didn't.

Here foo will have -fPIC added:

add_library(foo
    SHARED
    ${SRCS})
target_link_libraries(foo cpp-netlib_pic)


I've proved this to myself with make VERBOSE=1

[ 87%] Building CXX object
third_party/cpp-netlib/CMakeFiles/cpp-netlib_pic.dir/src/server_request_parsers_impl.cpp.o

/usr/bin/c++   ... -std=c++14 -Werror -Wall -Wextra ... -o
CMakeFiles/cpp-netlib_pic.dir/src/server_request_parsers_impl.cpp.o -c
.../third_party/cpp-netlib/src/server_request_parsers_impl.cpp

Note no -fPIC here.

When building a target which uses cpp-netlib_pic -fPIC appears:

[ 93%] Building CXX object foo.cc.o
/usr/bin/c++  ... -std=c++14 -Werror -Wall -Wextra ... *-fPIC* ... -o
CMakeFiles/foo_shared_lib.dir/foo.cc.o -c .../foo/foo.cc

How can I configure CMake to build the 1st library (cpp-netlib_pic) with
-fPIC?
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