Backport #3041 tailrec instances for StackSafeMonad and Defer to scala_2.11

[gagandeepkalra]

addresses #3143

[codecov-io]

Codecov Report

Merging #3332 into scala_2.11 will increase coverage by <.01%.
The diff coverage is 100%.

@@              Coverage Diff               @@
##           scala_2.11    #3332      +/-   ##
==============================================
+ Coverage       93.42%   93.43%   +<.01%     
==============================================
  Files             385      386       +1     
  Lines            7165     7173       +8     
  Branches          191      186       -5     
==============================================
+ Hits             6694     6702       +8     
  Misses            471      471

Impacted Files	Coverage Δ
core/src/main/scala/cats/Eval.scala	98.87% <100%> (+0.01%)	⬆️
core/src/main/scala/cats/instances/tailrec.scala	100% <100%> (ø)

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[travisbrown]

If MiMa says it's okay it looks good to me.