[lldb][test] Enable TestIRInterpreter on Windows

Relates to llvm#22139

This used to be broken because the expressions didn't work,
but the test also used getpid which isn't avaialable on Windows.

So when the expressions started working, evaluation still failed
due to getpid.

I made it call GetCurrentProcessId and it worked.

Author: DavidSpickett

lldb/test/API/commands/expression/ir-interpreter/TestIRInterpreter.py

@@ -105,8 +105,6 @@ def build_and_run(self):
         self.runCmd("run", RUN_SUCCEEDED)
 
     @add_test_categories(["pyapi"])
-    # getpid() is POSIX, among other problems, see bug
-    @expectedFailureAll(oslist=["windows"], bugnumber="http://llvm.org/pr21765")
     def test_ir_interpreter(self):
         self.build_and_run()
 
@@ -137,6 +135,14 @@ def test_ir_interpreter(self):
         for expression in set_up_expressions:
             self.frame().EvaluateExpression(expression, options)
 
+        func_call = "(int)getpid"
+        if lldbplatformutil.getPlatform() == "windows":
+            func_call = "(int)GetCurrentProcessId()"
+
+        for expression in expressions:
+            interp_expression = expression
+            jit_expression = func_call + "; " + expression
+
         for expression in expressions:
             interp_expression = expression
             jit_expression = "(int)getpid(); " + expression