Trac #29170: Fix R installation errors related to gfortran

As reported
- for 9.0.rc1 in https://groups.google.com/d/msg/sage-
release/YaedKjwMhzc/d44U0MM3BwAJ
- for 9.1.beta3 in https://groups.google.com/d/msg/sage-
release/xxEfql2Isgg/bV-FQN8VFQAJ
- for 9.1.beta8 in https://groups.google.com/d/msg/sage-
release/eMQIlhglN98/bTwDGD9HBQAJ

https://developer.r-project.org/Blog/public/2019/05/15/gfortran-issues-
with-lapack/index.html

URL: https://trac.sagemath.org/29170
Reported by: mkoeppe
Ticket author(s): Matthias Koeppe
Reviewer(s): Dima Pasechnik

build/pkgs/r/spkg-install.in

@@ -15,6 +15,12 @@ else
     CFLAGS="-g -O2 $CFLAGS"
     FCFLAGS="-g -O2 $FCFLAGS"
 fi
+# #29170: Compilation errors caused by a silently failing configure check
+# "for type of 'hidden' Fortran character lengths"
+# on ubuntu-bionic-minimal, ubuntu-eoan/focal-minimal, debian-buster/bullseye/sid-minimal,
+# linuxmint-19.3-minimal, archlinux-latest-minimal
+CFLAGS="$CFLAGS -fPIC"
+FCFLAGS="$FCFLAGS -fPIC"
 
 export CFLAGS CPPFLAGS FCFLAGS LDFLAGS