Add OpenSuse support for conf-mpfr-paths

[jmid]

Spotted in #28224 where apronext is now failing conf-mpfr-paths now that conf-gmp-paths was fixed in #28231:

#=== ERROR while compiling conf-mpfr-paths.1 ==================================#
# context              2.3.0 | linux/x86_64 | ocaml-base-compiler.5.3.0 | file:///home/opam/opam-repository
# path                 ~/.opam/5.3/.opam-switch/build/conf-mpfr-paths.1
# command              ~/.opam/opam-init/hooks/sandbox.sh build sh /home/opam/.opam/5.3/lib/ez-conf-lib/ez-conf-lib mpfr mpfr.h test-mpfr.c CPPFLAGS+=-I/usr/include LDFLAGS+=-L/usr/lib64 LIBS+=-lgmp --package-name conf-mpfr-paths -- /usr/local
# exit-code            1
# env-file             ~/.opam/log/conf-mpfr-paths-7-0e450a.env
# output-file          ~/.opam/log/conf-mpfr-paths-7-0e450a.out
### output ###
# checking compilation with gcc -O2 -fno-strict-aliasing -fwrapv  -pthread   -D_FILE_OFFSET_BITS=64 : working
# looking for mpfr without prefix
# include mpfr.h: not found
# looking for mpfr in prefix /usr/local
# looking for mpfr in prefix /usr
# looking for mpfr in prefix /usr/local
# library mpfr not found
# mpfr not found; pass further possible prefixes     	 after '--' on the command line

[jmid]

This only fails on Windows and a lint check. It should therefore be good to go 👍

[mseri]

Thanks