[lldb][AArch64] Only run MTE memory region test if we have MTE

This test is flakey because it tries to read the proc/smaps
file of the first lldb-server process it finds. This process
can finish before we finish doing that.

http://lab.llvm.org:8011/#/builders/96/builds/6634/steps/6/logs/stdio

For now limit this to MTE targets which basically means
QEMU via lldb-dotest, which doesn't have this issue.

I'll fix the race condition shortly.

lldb/test/API/linux/aarch64/mte_memory_region/TestAArch64LinuxMTEMemoryRegion.py

@@ -20,6 +20,8 @@ class AArch64LinuxMTEMemoryRegionTestCase(TestBase):
     @skipIf(archs=no_match(["aarch64"]))
     @skipUnlessPlatform(["linux"])
     def test_mte_regions(self):
+        if not self.isAArch64MTE():
+            self.skipTest('Target must support MTE.')
         if not self.hasLinuxVmFlags():
             self.skipTest('/proc/{pid}/smaps VmFlags must be present')