[llvm] [AArch64TargetParser]Fix reconstructFromParsedFeatures ignoring negative features (PR #142236)

[Tomas Matheson via llvm-commits]

================
@@ -1831,6 +1831,22 @@ TEST_P(AArch64ExtensionDependenciesBaseCPUTestFixture,
   }
 }
 
+TEST(TargetParserTest, testAArch64ReconstructFromParsedFeatures) {
----------------
tmatheson-arm wrote:

FYI, the failure of this test without the associated changes looks like this:

```
[ RUN      ] TargetParserTest.testAArch64ReconstructFromParsedFeatures
.../llvm/main/llvm/unittests/TargetParser/TargetParserTest.cpp:1843: Failure
Value of: NonExtensions
Expected: equals { "-Baz", "+FooBar" }
  Actual: { "-sve2", "-Baz", "+FooBar", "-sve" }, which has these unexpected elements: "-sve2", "-sve"

[  FAILED  ] TargetParserTest.testAArch64ReconstructFromParsedFeatures (0 ms)
```

and when that is fixed

```
[ RUN      ] TargetParserTest.testAArch64ReconstructFromParsedFeatures
.../llvm/main/llvm/unittests/TargetParser/TargetParserTest.cpp:1848: Failure
Value of: Features
Expected: equals { "+sve2", "+neon", "-sve" }
  Actual: { "+neon", "+sve", "+sve2" }, which has these unexpected elements: "+sve",
and doesn't have these expected elements: "-sve"

[  FAILED  ] TargetParserTest.testAArch64ReconstructFromParsedFeatures (0 ms)
```

https://github.com/llvm/llvm-project/pull/142236