Question:
Buildroot does not allow LD_LIBBRARY_PATH
Build/make user does not have root provilege.
Buildroot needs some extra so/lib for host side tool/QT build
Solution
[lake@localhost rk3399_linux_release_v2.5.1_20210301]$ ldd /data/sdb/lake/source/tmp/Firefly-rk3399_linux_release_v2.5.1_20210301/rk3399_linux_release_v2.5.1_20210301/buildroot/output/rockchip_rk3399/host/bin/qmlcachegen
linux-vdso.so.1 => (0x00007ffe63b7e000)
libatomic.so.1 => not found
librt.so.1 => /lib64/librt.so.1 (0x00007f4eac3bf000)
libdl.so.2 => /lib64/libdl.so.2 (0x00007f4eac1bb000)
libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f4eabf9f000)
libstdc++.so.6 => /lib64/libstdc++.so.6 (0x00007f4eabc97000)
libm.so.6 => /lib64/libm.so.6 (0x00007f4eab995000)
libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00007f4eab77f000)
libc.so.6 => /lib64/libc.so.6 (0x00007f4eab3bd000)
/lib64/ld-linux-x86-64.so.2 (0x00007f4eac5fa000)
[lake@localhost rk-linux-git]$ rpm2cpio libatomic-4.8.5-36.el7.x86_64.rpm | cpio -idmv ./usr/lib64/libatomic.so.1
./usr/lib64/libatomic.so.1.0.0
54 blocks
[lake@localhost rk-linux-git]$ pwd
/home/lake/extra/source/rk-linux-git
[lake@localhost rk-linux-git]$
[lake@localhost rk3399_linux_release_v2.5.1_20210301]$ patchelf --set-rpath /data/sdb/lake/source/rk-linux-git/usr/lib64/ /data/sdb/lake/source/tmp/Firefly-rk3399_linux_release_v2.5.1_20210301/rk3399_linux_release_v2.5.1_20210301/buildroot/output/rockchip_rk3399/host/bin/qmlcachegen [lake@localhost rk3399_linux_release_v2.5.1_20210301]$ ldd /data/sdb/lake/source/tmp/Firefly-rk3399_linux_release_v2.5.1_20210301/rk3399_linux_release_v2.5.1_20210301/buildroot/output/rockchip_rk3399/host/bin/qmlcachegen
linux-vdso.so.1 => (0x00007fff75d74000)
libatomic.so.1 => /data/sdb/lake/source/rk-linux-git/usr/lib64/libatomic.so.1 (0x00007f84f6d34000)
librt.so.1 => /lib64/librt.so.1 (0x00007f84f6afa000)
libdl.so.2 => /lib64/libdl.so.2 (0x00007f84f68f6000)
libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f84f66da000)
libstdc++.so.6 => /lib64/libstdc++.so.6 (0x00007f84f63d2000)
libm.so.6 => /lib64/libm.so.6 (0x00007f84f60d0000)
libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00007f84f5eba000)
libc.so.6 => /lib64/libc.so.6 (0x00007f84f5af8000)
/lib64/ld-linux-x86-64.so.2 (0x00007f84f6f3d000)
[lake@localhost rk3399_linux_release_v2.5.1_20210301]$