community/R: add musl-dev to -dev dependencies

I might be missing something here and I certainly don't want to add an
unnecessary dependency if there are use-cases for using R-dev without
musl-dev, but I can't figure out how you could actually use R-dev for
anything without musl-dev installed.

The header files installed by R-dev depend on the standard library, so
that any attempt to compile using the R-dev header files will fail with e.g.

    /usr/include/R/Rinternals.h:39:11: fatal error: stdio.h: No such file or directory
       39 | # include <stdio.h>
          |           ^~~~~~~~~

community/R/APKBUILD

@@ -3,14 +3,14 @@
 # Maintainer: Jakub Jirutka <jakub@jirutka.cz>
 pkgname=R
 pkgver=4.1.0
-pkgrel=1
+pkgrel=2
 pkgdesc="Language and environment for statistical computing"
 url="https://www.r-project.org/"
 # mips64 and riscv64 blocked by java-jre-headless
 arch="all !mips64 !riscv64"
 license="(GPL-2.0-only OR GPL-3.0-only) AND LGPL-2.1-or-later"
 depends="$pkgname-mathlib"
-depends_dev="gcc gfortran icu-dev libjpeg-turbo libpng-dev make openblas-dev>=0.3.0
+depends_dev="gcc gfortran icu-dev libjpeg-turbo libpng-dev make musl-dev openblas-dev>=0.3.0
 	pcre2-dev readline-dev xz-dev zlib-dev bzip2-dev curl-dev>=7.28
 	"
 makedepends="$depends_dev cairo-dev libxmu-dev java-jre-headless pango-dev