makeBinaryWrapper: Fix chdir golden test for darwin

On macOS, /tmp is a symlink to /private/tmp. When performing cd /tmp, and checking cwd - it won't match since it follows the symlink.

This caused test breakage on macOS but not Linux. Instead, use a folder which is not a symlink, and consistent across Linux and macOS.

pkgs/test/make-binary-wrapper/chdir.c

@@ -5,7 +5,7 @@
 #define assert_success(e) do { if ((e) < 0) { perror(#e); abort(); } } while (0)
 
 int main(int argc, char **argv) {
-    assert_success(chdir("/tmp/foo"));
+    assert_success(chdir("./tmp/foo"));
     argv[0] = "/send/me/flags";
     return execv("/send/me/flags", argv);
 }

pkgs/test/make-binary-wrapper/chdir.cmdline

@@ -1 +1 @@
-    --chdir /tmp/foo
+    --chdir ./tmp/foo

pkgs/test/make-binary-wrapper/chdir.env

@@ -1,2 +1,2 @@
-CWD=/tmp/foo
+CWD=SUBST_CWD/tmp/foo
 SUBST_ARGV0

pkgs/test/make-binary-wrapper/default.nix

@@ -6,7 +6,7 @@ let
     ${gcc}/bin/cc -Wall -Werror -Wpedantic -o $out ${./envcheck.c}
   '';
   makeGoldenTest = testname: runCommand "test-wrapper_${testname}" env ''
-    mkdir -p /tmp/foo
+    mkdir -p ./tmp/foo
 
     params=$(<"${./.}/${testname}.cmdline")
     eval "makeCWrapper /send/me/flags $params" > wrapper.c