Build against glibc 2.17 for RHEL/CentOS 7.x

[kim0]

Currently trying to run the binary fails

./dust
./dust: /lib64/libc.so.6: version `GLIBC_2.18' not found (required by ./dust)
[root@sim-0 dust-v0.7.1.alpha4-x86_64-unknown-linux-gnu]# rpm -q glibc
glibc-2.17-325.el7_9.x86_64
glibc-2.17-325.el7_9.i686

[bootandy]

that's glibc-2.17 the message says it needs glibc-2.18