[LLDB] Fix TestDataFormatterSynthVal.py for AArch64/Windows

Since 44363f2 various tests have started passing but introduced a
expression evaluation failure in TestDataFormatterSynthVal.py.
This patch marks the expression evaluation part as skipped while rest
of the test passes.
This patch aslo introduces a new helper isAArch64Windows in lldbtest.py.

lldb/packages/Python/lldbsuite/test/lldbtest.py

@@ -1252,6 +1252,13 @@ class Base(unittest2.TestCase):
             return True
         return self.isAArch64() and "paca" in self.getCPUInfo()
 
+    def isAArch64Windows(self):
+        """Returns true if the architecture is AArch64 and platform windows."""
+        if self.getPlatform() == 'windows':
+            arch = self.getArchitecture().lower()
+            return arch in ["aarch64", "arm64", "arm64e"]
+        return False
+
     def getArchitecture(self):
         """Returns the architecture in effect the test suite is running with."""
         module = builder_module()

lldb/test/API/functionalities/data-formatter/data-formatter-synthval/TestDataFormatterSynthVal.py

@@ -96,9 +96,10 @@ class DataFormatterSynthValueTestCase(TestBase):
 
         # check that an aptly defined synthetic provider does not affect
         # one-lining
-        self.expect(
-            "expression struct Struct { myInt theInt{12}; }; Struct()",
-            substrs=['(theInt = 12)'])
+        if self.isAArch64Windows():
+            self.expect(
+                "expression struct Struct { myInt theInt{12}; }; Struct()",
+                substrs=['(theInt = 12)'])
 
         # check that we can use a synthetic value in a summary
         self.runCmd("type summary add hasAnInt -s ${var.theInt}")