fetchsvn: set LC_ALL in builder to allow svn to handle unicode filenames

pkgs/build-support/fetchsvn/builder.sh

···
     export HOME="$PWD"
 fi;
 
+if test -z "$LC_ALL"; then
+    export LC_ALL="en_US.UTF-8"
+fi;
+
 # Pipe the "p" character into Subversion to force it to accept the
 # server's certificate.  This is perfectly safe: we don't care
 # whether the server is being spoofed --- only the cryptographic

pkgs/build-support/fetchsvn/default.nix

···
-{stdenv, subversion, sshSupport ? false, openssh ? null}:
+{stdenv, subversion, glibcLocales, sshSupport ? false, openssh ? null}:
 {url, rev ? "HEAD", md5 ? "", sha256 ? "",
  ignoreExternals ? false, ignoreKeywords ? false, name ? null}:
 
···
 stdenv.mkDerivation {
   name = name_;
   builder = ./builder.sh;
-  buildInputs = [subversion];
+  buildInputs = [ subversion glibcLocales ];
 
   outputHashAlgo = "sha256";
   outputHashMode = "recursive";