MPFR test failure on windows

[JeffBezanson]

e.g. https://build.julialang.org/#/builders/65/builds/743/steps/5/logs/stdio

Error in testset mpfr:
Test Failed at C:\buildbot\worker-tabularasa\tester_win64\build\share\julia\test\mpfr.jl:609
  Expression: log2(x) == log2(42)
   Evaluated: 5.3923174227787607 == 5.39231742277876

[DilumAluthge]

Duplicate of #41417.

After #41473, this test should be disabled on master. If you are seeing this in a PR build, can you trying rebasing the PR branch on the latest master?