Currently gmp.pc, which may be provided at least on some platforms, is not used at all -- neither by configure nor by sage.env.cython_aliases, sage.misc.cython.

For example, on homebrew, using it will provide the specific library search directory -L/usr/local/Cellar/gmp/6.2.1/lib instead of having to rely on /usr/local/ (which is disabled when compiler/linker are invoked with -isysroot)

Currently, gmp is detected using AC_CHECK_HEADER, and the result is communicated to sage-build-env-config as variables SAGE_GMP_PREFIX and SAGE_GMP_INCLUDE; but it is not available in the runtime environment (sage_conf.py, sage-env-config).

The failures reported in

• #31335 comment:47
• https://groups.google.com/g/sage-release/c/6WjKQt_e_B8/m/H2I4HZ-YCwAJ (https://groups.google.com/g/sage-release/c/6WjKQt_e_B8/m/Uut_ZRaZCwAJ)
• https://groups.google.com/g/sage-release/c/0q3kywk7RP8/m/uspq0xeuAgAJ
  can be fixed by simply changing sage.misc.cython to pick up gmp.pc. But to avoid unpleasant surprises, we need to make sure that it is used consistently when present.

(After #32549, the relevant file is build/pkgs/gmp/spkg-configure.m4.)

The above applies to mpfr as well. See failure report in https://groups.google.com/g/sage-release/c/8ctwsUGl6LQ/m/Ob38Iyh1AAAJ

Similar situation with readline (#29000): The spkg-configure script already uses pkg-config - but forgets to tell the build system what it found.

Previous tickets: #27212

Depends on #31344
Depends on #32549

CC: @dimpase @jhpalmieri @zlscherr @orlitzky

Component: build: configure

Keywords: mpfr

Branch/Commit: u/gh-zlscherr/add_gmp_mpfr_cython @ 07e00b6

Issue created by migration from https://trac.sagemath.org/ticket/31348