From: Eric Joldasov <bratishkaerik@landless-city.net>

# Moved here from old version of https://github.com/gentoo/gentoo/pull/37283 .

Patch for the purposes of cross-compiling support in "zig-build".
Solves following errors when passing "--search-prefix /" when
NOT cross-compiling on "default/linux/amd64/23.0/desktop/plasma" profile:

```
error: ld.lld: /../Scrt1.o is incompatible with elf32-i386
error: ld.lld: /../crti.o is incompatible with elf32-i386
error: ld.lld: /../zig-cache/local/../ncdu.o is incompatible with elf32-i386
error: ld.lld: /../zig-cache/global/../libcompiler_rt.a is incompatible with elf32-i386
error: ld.lld: /../crtn.o is incompatible with elf32-i386
error: the following command failed with 5 compilation errors:
```

Add "lib64" and "lib32" directories (depends on "usize" bitsize on system) before "lib"
when using "--search-prefix" so that libraries from lib64/lib32 are not overwritten by
libraries from "lib" which can have different bitwidth.

Ideally it should be unified with logic in std.zig.NativePaths (and maybe aro.toolchains.Linux?).
Also would be nice to have separate "--search-bin-prefix", "--search-lib-prefix",
and "--search-include-prefix" to pass exact directories for finding binaries,
libraries and headers, because we might want to search /usr/bin for binaries
that are run during build.zig logic (BDEPEND on Gentoo) while searching in 
/usr/different-target/{lib64,include} for libraries and headers that used for
compiled artifacts (DEPEND/RDEPEND on Gentoo).

diff --git a/lib/std/Build/Step/Compile.zig b/lib/std/Build/Step/Compile.zig
index d18d8de413..ff69585c69 100644
--- a/lib/std/Build/Step/Compile.zig
+++ b/lib/std/Build/Step/Compile.zig
@@ -1595,17 +1595,6 @@ fn make(step: *Step, prog_node: std.Progress.Node) !void {
         // This prevents a warning, that should probably be upgraded to an error in Zig's
         // CLI parsing code, when the linker sees an -L directory that does not exist.
 
-        if (prefix_dir.accessZ("lib", .{})) |_| {
-            try zig_args.appendSlice(&.{
-                "-L", b.pathJoin(&.{ search_prefix, "lib" }),
-            });
-        } else |err| switch (err) {
-            error.FileNotFound => {},
-            else => |e| return step.fail("unable to access '{s}/lib' directory: {s}", .{
-                search_prefix, @errorName(e),
-            }),
-        }
-
         if (prefix_dir.accessZ("include", .{})) |_| {
             try zig_args.appendSlice(&.{
                 "-I", b.pathJoin(&.{ search_prefix, "include" }),
@@ -1616,6 +1605,36 @@ fn make(step: *Step, prog_node: std.Progress.Node) !void {
                 search_prefix, @errorName(e),
             }),
         }
+
+        blk: {
+            const lib_arch_dir = switch (compile.rootModuleTarget().ptrBitWidth()) {
+                64 => "lib64",
+                32 => "lib32",
+                // Can't find info on whether "lib16" or "lib128" exist, but for Gentoo this should be enough.
+                else => break :blk,
+            };
+            if (prefix_dir.accessZ(lib_arch_dir, .{})) |_| {
+                try zig_args.appendSlice(&.{
+                    "-L", b.pathJoin(&.{ search_prefix, lib_arch_dir }),
+                });
+            } else |err| switch (err) {
+                error.FileNotFound => break :blk,
+                else => |e| return step.fail("unable to access '{s}/{s}' directory: {s}", .{
+                    lib_arch_dir, search_prefix, @errorName(e),
+                }),
+            }
+        }
+
+        if (prefix_dir.accessZ("lib", .{})) |_| {
+            try zig_args.appendSlice(&.{
+                "-L", b.pathJoin(&.{ search_prefix, "lib" }),
+            });
+        } else |err| switch (err) {
+            error.FileNotFound => {},
+            else => |e| return step.fail("unable to access '{s}/lib' directory: {s}", .{
+                search_prefix, @errorName(e),
+            }),
+        }
     }
 
     if (compile.rc_includes != .any) {