From: Eric Joldasov <bratishkaerik@getgoogleoff.me>

Install 'zig' binary in 'build_dir/stage3' directory so that we can find it and use for testing.
Also split "add_custom_target(stage3 ALL" and command that it invokes, so that it won't retry it during installation,
as target will be considered not out-of-date. (Bug https://bugs.gentoo.org/890457 and https://bugs.gentoo.org/890459).
Upstream PR https://github.com/ziglang/zig/pull/14255.

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1094,10 +1094,14 @@ set(ZIG_BUILD_ARGS
 )
 
 add_custom_target(stage3 ALL
-    COMMAND zig2 build compile ${ZIG_BUILD_ARGS}
-    DEPENDS zig2
-    COMMENT STATUS "Building stage3"
-    WORKING_DIRECTORY "${CMAKE_SOURCE_DIR}"
+  DEPENDS "${CMAKE_BINARY_DIR}/stage3/bin/zig"
+)
+
+add_custom_command(
+  OUTPUT "${CMAKE_BINARY_DIR}/stage3/bin/zig"
+  COMMAND zig2 build --prefix "${CMAKE_BINARY_DIR}/stage3" ${ZIG_BUILD_ARGS}
+  COMMENT STATUS "Building stage3"
+  WORKING_DIRECTORY "${CMAKE_SOURCE_DIR}"
 )
 
 install(CODE "set(ZIG_EXECUTABLE \"${ZIG_EXECUTABLE}\")")

--- a/build.zig
+++ b/build.zig
@@ -148,10 +148,6 @@ pub fn build(b: *Builder) !void {
     };
 
     const exe = b.addExecutable("zig", main_file);
-
-    const compile_step = b.step("compile", "Build the self-hosted compiler");
-    compile_step.dependOn(&exe.step);
-
     exe.stack_size = stack_size;
     exe.strip = strip;
     exe.sanitize_thread = sanitize_thread;