The goal of this ticket is to

• package Kim Walish's primecount package (the version of prime_pi
  in Sage has bugs, see Fix prime_pi errors and make primecount standard #24960)
• provide an experimental interface to it in arith/prime_pi.pyx (that will
  be merged with the current prime_pi in Sage in update and promote spkg primecount #25009).

Note that

• primecount's build system uses cmake, which needs an upgrade (see Upgrade cmake to 3.11.0 #25109)
• the latest release of primecount should work on both big-endian and little-indian
  processors but has been tested successfully
• linking on Mac OSX looks fishy but seems to work fine

Tarball (to be renamed primecount-4.3.tar.gz in Sage):

• https://github.com/kimwalisch/primecount/archive/v4.3.tar.gz

This ticket led to opening and solving an upstream issue,
leading to improvements in the build and documentation:

• make install fail kimwalisch/primecount#11

Depends on #25109

CC: @jpflori @kiwifb @vinklein @slel

Component: packages: optional

Keywords: thursdaysbdx

Author: Vincent Delecroix

Branch/Commit: 6f73fad

Reviewer: Vincent Klein, François Bissey

Issue created by migration from https://trac.sagemath.org/ticket/24966