freebsd: Fix cross compilation

It looks like upgrading to newer clang has caused some `-Werror`
problems. We should probably disable `-Werror` entirely, but for now,
I've done the more targetted fix of disabling one specific warning, and
sending freebsd/freebsd-src#1882 upstream.

Author: Ericson2314

pkgs/os-specific/bsd/freebsd/pkgs/libthr.nix

@@ -1,6 +1,7 @@
 {
   lib,
   stdenv,
+  fetchpatch,
   mkDerivation,
   libcMinimal,
   include,
@@ -32,6 +33,19 @@ mkDerivation {
     libgcc
   ];
 
+  patches = [
+    # https://github.com/freebsd/freebsd-src/pull/1882
+    (fetchpatch {
+      name = "freebsd-libthr-use-nonstring-attribute.patch";
+      url = "https://github.com/freebsd/freebsd-src/pull/1882/commits/650800993deb513dc31e99ef5cdecd50ee70bb04.diff";
+      hash = "sha256-WKN7dfGAs1+XADT4aLUkkKmQQ4n7gsyFUTCeo6mcuMY=";
+      includes = [ "lib/libthr/thread/thr_printf.c" ];
+    })
+  ];
+
+  # Presumably newer Clang has gotten more strict.
+  CWARNEXTRA = "-Wno-cast-function-type-mismatch";
+
   preBuild = ''
     export NIX_CFLAGS_COMPILE="$NIX_CFLAGS_COMPILE -B${csu}/lib"
   '';

pkgs/os-specific/bsd/freebsd/pkgs/rtld-elf.nix

@@ -1,5 +1,6 @@
 {
   mkDerivation,
+  fetchpatch,
   include,
   rpcgen,
   flex,
@@ -30,6 +31,16 @@ mkDerivation {
   ]
   ++ extraSrc;
 
+  patches = [
+    # https://github.com/freebsd/freebsd-src/pull/1882
+    (fetchpatch {
+      name = "freebsd-rtld-use-nonstring-attribute.patch";
+      url = "https://github.com/freebsd/freebsd-src/pull/1882/commits/650800993deb513dc31e99ef5cdecd50ee70bb04.diff";
+      hash = "sha256-V9jDE/5Fu6hLIzlG1e6AqLnGwlzW2OjonyUgvSVtm58=";
+      includes = [ "libexec/rtld-elf/rtld.c" ];
+    })
+  ];
+
   outputs = [
     "out"
     "man"