Make it possible to disable build of r, rpy2 using ./configure --disable-r #31409
Description
Prompted by a build failure of r on cygwin-standard in https://github.com/mkoeppe/sage/runs/1915093157
[r-3.6.3] blas.o: in function `dsymm_':
[r-3.6.3] /opt/sage-1e693c9ae51a53dad0fe099efc41439dc898f02f/var/tmp/sage/build/r-3.6.3/src/src/extra/blas/blas.f:2986:(.text+0x4352): relocation truncated to fit: R_X86_64_PC32 against undefined symbol `xerbla_'
we make it possible to disable R using a configure options so that one can get a working Sage installation in this way.
(The original build failure has hopefully resolved been resolved by #29537.)
Previous tickets and discussions:
- cygwin: Do not use system R #29486
- upgrade rpy2 package 2.8.2 -> 3.3.5, upgrade R to 3.6.3, add new dependencies #29441
- Fix R installation errors related to gfortran #29170
- https://groups.google.com/g/sage-devel/c/IX3niEdmCEM/m/LovmF6gmIwAJ
- https://wiki.sagemath.org/ReleaseTours/sage-9.2#rpy2_and_R
- https://groups.google.com/g/sage-devel/c/alkG4veIsBk/m/432cxzpYAQAJ
Depends on #29537
Depends on #30383
CC: @embray @dimpase @orlitzky @jhpalmieri @kiwifb @novoselt @EmmanuelCharpentier @videlec @kliem
Component: porting: Cygwin
Author: Matthias Koeppe
Branch/Commit: f04c134
Reviewer: François Bissey, John Palmieri
Issue created by migration from https://trac.sagemath.org/ticket/31409