Revert "Show a clear error on -o pointing to an invalid directory. fixes

 emscripten-core#8549 (emscripten-core#8551)"

This reverts commit 5d7247b.

emcc.py

@@ -712,13 +712,6 @@ def uniquename(name):
   # specified_target is the user-specified one, target is what we will generate
   if specified_target:
     target = specified_target
-    # check for the existence of the output directory now, to avoid having
-    # to do so repeatedly when each of the various output files (.mem, .wasm,
-    # etc) are written. This gives a more useful error message than the
-    # IOError and python backtrace that users would otherwise see.
-    dirname = os.path.dirname(target)
-    if dirname and not os.path.isdir(dirname):
-      exit_with_error("specified output file (%s) is in a directory that does not exist" % target)
   else:
     target = 'a.out.js'
 

tests/test_other.py

@@ -7847,10 +7847,6 @@ def test_invalid_mem(self):
     ret = self.expect_fail([PYTHON, EMCC, path_from_root('tests', 'hello_world.c'), '-s', 'WASM_MEM_MAX=33MB+1'])
     self.assertContained('WASM_MEM_MAX must be a multiple of 64KB', ret)
 
-  def test_invalid_output_dir(self):
-    ret = self.expect_fail([PYTHON, EMCC, path_from_root('tests', 'hello_world.c'), '-o', os.path.join('NONEXISTING_DIRECTORY', 'out.js')])
-    self.assertContained('specified output file (NONEXISTING_DIRECTORY%sout.js) is in a directory that does not exist' % os.path.sep, ret)
-
   @unittest.skipIf(SPIDERMONKEY_ENGINE not in JS_ENGINES, 'cannot run without spidermonkey')
   def test_binaryen_ctors(self):
     # ctor order must be identical to js builds, deterministically