Bitcoin Core private

After #19685 started setting LDFLAGS, the INSTALL_RPATH_USE_LINK_PATH cmake option used in the libmultiprocess build no longer works, so it is neccessary to set CMAKE_INSTALL_RPATH as a fallback. It's unclear currently whether the bad interaction between INSTALL_RPATH_USE_LINK_PATH and LDFLAGS is a bug, but the issue is reported: https://github.com/bitcoin/bitcoin/issues/19981#issuecomment-696680877 https://discourse.cmake.org/t/install-rpath-use-link-path-not-working-when-cmake-exe-linker-flags-ldflags-is-set/1892 Commands useful for building / testing this change make -C depends MULTIPROCESS=1 print-libmultiprocess_cmake make -C depends MULTIPROCESS=1 print-native_libmultiprocess_cmake make -C depends MULTIPROCESS=1 HOST=x86_64-apple-darwin16 print-libmultiprocess_cmake rm -rvf depends/x86_64-pc-linux-gnu/native depends/work/staging depends/work/build make -C depends MULTIPROCESS=1 V=1 native_libmultiprocess_staged for f in `find -name mpgen`; do echo == $f ==; readelf -d $f | grep -i path; done make -C depends MULTIPROCESS=1 V=1 native_libmultiprocess_built find -name CMakeCache.txt Fixes #19981