constants: Protect F which is defined as a macro by some frameworks - part 2

[cbicari]

This is the twin sibling of : #1391

The same issue occurs with unprotected macro.
Had forgotten this one in previous correction.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.35%. Comparing base (f49ab98) to head (51efb17).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1396   +/-   ##
========================================
  Coverage    95.35%   95.35%           
========================================
  Files          825      825           
  Lines        68223    68223           
========================================
+ Hits         65051    65054    +3     
+ Misses        3172     3169    -3     

Files with missing lines	Coverage Δ
include/boost/math/constants/constants.hpp	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

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