Process chdir option sooner so execFillarg sees it

This is a bit hacky due to the way we handle chdir on top of
posix_spawn. The logic for making the command line use sh and cd
lives in execFillarg, since it must handle the case where the
virtual CWD is not the same as the JVM CWD. In order to make sure
that processing also happens for incoming chdir: options, this
patch pre-processes the options hash just for chdir.

Fixes jruby#8126

core/src/main/java/org/jruby/util/io/PopenExecutor.java

@@ -87,7 +87,7 @@ public static RubyFixnum spawn(ThreadContext context, IRubyObject[] argv) {
         ExecArg eargp;
         IRubyObject fail_str;
 
-        eargp = execargNew(context, argv, true, false);
+        eargp = execargNew(context, argv, context.nil, true, false);
         execargFixup(context, runtime, eargp);
         fail_str = eargp.use_shell ? eargp.command_name : eargp.command_name;
 
@@ -110,7 +110,7 @@ public IRubyObject systemInternal(ThreadContext context, IRubyObject[] argv, Str
         ExecArg eargp;
         long pid;
 
-        eargp = execargNew(context, argv, true, true);
+        eargp = execargNew(context, argv, context.nil, true, true);
         execargFixup(context, runtime, eargp);
         pid = spawnProcess(context, runtime, eargp, errmsg);
 
@@ -297,7 +297,7 @@ public static IRubyObject pipeOpen(ThreadContext context, IRubyObject prog, Stri
         ExecArg execArg = null;
 
         if (!isPopenFork(context.runtime, (RubyString)prog))
-            execArg = execargNew(context, argv, true, false);
+            execArg = execargNew(context, argv, context.nil, true, false);
         return new PopenExecutor().pipeOpen(context, execArg, modestr, fmode, convconfig);
     }
 
@@ -340,14 +340,14 @@ public static IRubyObject popen(ThreadContext context, IRubyObject[] argv, RubyC
 //            #endif
             tmp = ((RubyArray)tmp).aryDup();
             //            RBASIC_CLEAR_CLASS(tmp);
-            eargp = execargNew(context, ((RubyArray)tmp).toJavaArray(), false, false);
+            eargp = execargNew(context, ((RubyArray)tmp).toJavaArray(), opt, false, false);
             ((RubyArray)tmp).clear();
         } else {
             pname = pname.convertToString();
             eargp = null;
             if (!isPopenFork(runtime, (RubyString)pname)) {
                 IRubyObject[] pname_p = {pname};
-                eargp = execargNew(context, pname_p, true, false);
+                eargp = execargNew(context, pname_p, opt, true, false);
                 pname = pname_p[0];
             }
         }
@@ -1678,14 +1678,14 @@ static RubyArray checkExecRedirect1(Ruby runtime, RubyArray ary, IRubyObject key
     private static final int ST_STOP = 1;
 
     // rb_execarg_new
-    public static ExecArg execargNew(ThreadContext context, IRubyObject[] argv, boolean accept_shell, boolean allow_exc_opt) {
+    public static ExecArg execargNew(ThreadContext context, IRubyObject[] argv, IRubyObject optForChdir, boolean accept_shell, boolean allow_exc_opt) {
         ExecArg eargp = new ExecArg();
-        execargInit(context, argv, accept_shell, eargp, allow_exc_opt);
+        execargInit(context, argv, optForChdir, accept_shell, eargp, allow_exc_opt);
         return eargp;
     }
 
     // rb_execarg_init
-    private static RubyString execargInit(ThreadContext context, IRubyObject[] argv, boolean accept_shell, ExecArg eargp, boolean allow_exc_opt) {
+    private static RubyString execargInit(ThreadContext context, IRubyObject[] argv, IRubyObject optForChdir, boolean accept_shell, ExecArg eargp, boolean allow_exc_opt) {
         RubyString prog, ret;
         IRubyObject[] env_opt = {context.nil, context.nil};
         IRubyObject[][] argv_p = {argv};
@@ -1698,6 +1698,14 @@ private static RubyString execargInit(ThreadContext context, IRubyObject[] argv,
             optHash = optHash.dupFast(context);
             exception = optHash.delete(context, exceptionSym);
         }
+
+        RubySymbol chdirSym = context.runtime.newSymbol("chdir");
+        IRubyObject chdir;
+        if (!optForChdir.isNil() && (chdir = ((RubyHash) optForChdir).delete(chdirSym)) != null) {
+            eargp.chdirGiven = true;
+            eargp.chdir_dir = chdir.convertToString().toString();
+        }
+
         execFillarg(context, prog, argv_p[0], env_opt[0], env_opt[1], eargp);
         if (exception.isTrue()) {
             eargp.exception = true;