Add signal handler to catch SIGFPE on the GMP 6.3+

[skirpichev]

Since 6.3.0 some memory errors in mpz/realloc.c trigger SIGFPE exception. I think it's an upstream bug: helpful message should be emitted instead.

This patch install SIGFPE handler, that does this.

Closes #497

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Codecov Report

Attention: Patch coverage is 25.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 85.59%. Comparing base (224745b) to head (dfaae94).
Report is 46 commits behind head on master.

Files with missing lines	Patch %	Lines
src/gmpy2.c	25.00%	3 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #513      +/-   ##
==========================================
+ Coverage   85.52%   85.59%   +0.06%     
==========================================
  Files          50       50              
  Lines       11656    11660       +4     
  Branches     2202     2202              
==========================================
+ Hits         9969     9980      +11     
+ Misses       1687     1680       -7     

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[skirpichev]

GMP_ERROR_DIVISION_BY_ZERO and GMP_ERROR_SQRT_OF_NEGATIVE, in principle, shouldn't be triggered by some code in the gmpy2 codebase. Maybe I should check only GMP_ERROR_MPZ_OVERFLOW?

[casevh]

GMP_ERROR_DIVISION_BY_ZERO and GMP_ERROR_SQRT_OF_NEGATIVE, in principle, shouldn't be triggered by some code in the gmpy2 codebase. Maybe I should check only GMP_ERROR_MPZ_OVERFLOW?

While GMP_ERROR_DIVISION_BY_ZERO and GMP_ERROR_SQRT_OF_NEGATIVE shouldn't occur, I think it's fine to catch all the errors.