Math::BigFloat can swap the library it uses, have you tried 'GMP' ?

 use Math::BigFloat lib => 'GMP';
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AFIACT that calls Math::BigInt::GMP so you'll need to install that too.

use Math::BigInt;

  # or make it faster with huge numbers: install (optional)
  # Math::BigInt::GMP and always use (it will fall back to
  # pure Perl if the GMP library is not installed):
  # (See also the L<MATH LIBRARY> section!)

  # will warn if Math::BigInt::GMP cannot be found
  use Math::BigInt lib => 'GMP';
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