build: force use of LLVM Linker (lld) and fix usage of -dead_strip on Linux

internal/build/build.go

@@ -286,14 +286,19 @@ func linkMainPkg(pkg *packages.Package, pkgs []*aPackage, runtimeFiles []string,
 	if app == "" {
 		app = filepath.Join(conf.BinPath, name+conf.AppExt)
 	}
-	const N = 5
+	const N = 6
 	args := make([]string, N, len(pkg.Imports)+len(runtimeFiles)+(N+1))
 	args[0] = "-o"
 	args[1] = app
 	args[2] = "-Wno-override-module"
-	args[3] = "-Xlinker"
-	args[4] = "-dead_strip"
-	//args[5] = "-O2"
+	args[3] = "-fuse-ld=lld"
+	args[4] = "-Xlinker"
+	if runtime.GOOS == "darwin" { // ld64.lld (macOS)
+		args[5] = "-dead_strip"
+	} else { // ld.lld (Unix), lld-link (Windows), wasm-ld (WebAssembly)
+		args[5] = "--gc-sections"
+	}
+	//args[6] = "-O2"
 	needRuntime := false
 	needPyInit := false
 	packages.Visit([]*packages.Package{pkg}, nil, func(p *packages.Package) {