r-cran-rstan/2.21.8-1 does not build on armhf

[Lucas Kanashiro]

This is the important part of the build failure log:

g++ -std=gnu++14 -I"/usr/share/R/include" -DNDEBUG -I"../inst/include" -I"../inst/include/boost_not_in_BH" -I"." -DBOOST_DISABLE_ASSERTS -DBOOST_PHOENIX_NO_VARIADIC_EXPRESSION -DBOOST_NO_AUTO_PTR -D_REENTRANT -DSTAN_THREADS -I'/usr/lib/R/site-library/Rcpp/include' -I'/usr/lib/R/site-library/RcppEigen/include' -I'/usr/lib/R/site-library/BH/include' -I'/usr/lib/R/site-library/StanHeaders/include' -I'/usr/lib/R/site-library/RcppParallel/include' -fpic -g -O2 -ffile-prefix-map=/build/r-base-8bYJBo/r-base-4.2.2.20221110=. -fstack-protector-strong -Wformat -Werror=format-security -fdebug-prefix-map=/build/r-base-8bYJBo/r-base-4.2.2.20221110=/usr/src/r-base-4.2.2.20221110-2build1 -Wdate-time -D_FORTIFY_SOURCE=2 -c grammar_inst.cpp -o grammar_inst.o
virtual memory exhausted: Cannot allocate memory
make[1]: *** [/usr/lib/R/etc/Makeconf:178: grammar_inst.o] Error 1

This issue was already reported upstream by the Debian maintainer here:

https://github.com/stan-dev/rstan/issues/1032

Apparently, it builds fine in armhf if we use libboost >= 1.81 (what they have in CRAN). Since we do not have that until Lunar it FTBFS.