guile: workaround for libunistring / darwin libiconv

guile will fail in the configure phase on darwin due to libunistring not
building with libiconv as libunistring 1.3 rejects darwin's libiconv
implementation. Work around this by using the gnu libiconv.

https://lists.gnu.org/archive/html/bug-gnulib/2024-05/msg00375.html

pkgs/development/interpreters/guile/2.0.nix

@@ -11,15 +11,22 @@
   libffi,
   libtool,
   libunistring,
+  libiconvReal,
   makeWrapper,
   pkg-config,
   pkgsBuildBuild,
   readline,
-}:
+}@args:
 
 let
   # Do either a coverage analysis build or a standard build.
   builder = if coverageAnalysis != null then coverageAnalysis else stdenv.mkDerivation;
+  # workaround for libiconv bug in macOS 14/15
+  libunistring =
+    if stdenv.hostPlatform.isDarwin then
+      args.libunistring.override { libiconv = libiconvReal; }
+    else
+      args.libunistring;
 in
 builder rec {
   pname = "guile";

pkgs/development/interpreters/guile/2.2.nix

@@ -11,15 +11,22 @@
   libffi,
   libtool,
   libunistring,
+  libiconvReal,
   makeWrapper,
   pkg-config,
   pkgsBuildBuild,
   readline,
-}:
+}@args:
 
 let
   # Do either a coverage analysis build or a standard build.
   builder = if coverageAnalysis != null then coverageAnalysis else stdenv.mkDerivation;
+  # workaround for libiconv bug in macOS 14/15
+  libunistring =
+    if stdenv.hostPlatform.isDarwin then
+      args.libunistring.override { libiconv = libiconvReal; }
+    else
+      args.libunistring;
 in
 builder rec {
   pname = "guile";

pkgs/development/interpreters/guile/3.0.nix

@@ -11,17 +11,24 @@
   libffi,
   libtool,
   libunistring,
+  libiconvReal,
   libxcrypt,
   makeWrapper,
   pkg-config,
   pkgsBuildBuild,
   readline,
   writeScript,
-}:
+}@args:
 
 let
   # Do either a coverage analysis build or a standard build.
   builder = if coverageAnalysis != null then coverageAnalysis else stdenv.mkDerivation;
+  # workaround for libiconv bug in macOS 14/15
+  libunistring =
+    if stdenv.hostPlatform.isDarwin then
+      args.libunistring.override { libiconv = libiconvReal; }
+    else
+      args.libunistring;
 in
 builder rec {
   pname = "guile";