Reenable "Always import constants" after compile time fixes
I re-measured thin link times for a number of binaries that had compile
time explosions with importing of constants previously and confirmed
they no longer have any notable increases with it enabled.
Reviewers: wmi, evgeny777
Subscribers: hiraditya, arphaman, llvm-commits
Differential Revision: https://reviews.llvm.org/D74512