[llvm][unittests] Put human-readable names on TargetParserTests. NFC (#80749)

Before:
```
[----------] 65 tests from AArch64CPUTests/AArch64CPUTestFixture
[ RUN      ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/0
[       OK ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/0 (0 ms)
[ RUN      ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/1
[       OK ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/1 (0 ms)
[ RUN      ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/2
[       OK ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/2 (0 ms)
[ RUN      ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/3
[       OK ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/3 (0 ms)
[ RUN      ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/4
[       OK ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/4 (0 ms)
[ RUN      ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/5
[       OK ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/5 (0 ms)
[ RUN      ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/6
[       OK ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/6 (0 ms)
[ RUN      ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/7
[       OK ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/7 (0 ms)
[ RUN      ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/8
...
```

After:
```
[----------] 65 tests from AArch64CPUTests/AArch64CPUTestFixture
[ RUN      ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/cortex_a34
[       OK ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/cortex_a34 (0 ms)
[ RUN      ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/cortex_a35
[       OK ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/cortex_a35 (0 ms)
[ RUN      ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/cortex_a53
[       OK ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/cortex_a53 (0 ms)
[ RUN      ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/cortex_a55
[       OK ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/cortex_a55 (0 ms)
[ RUN      ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/cortex_a510
[       OK ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/cortex_a510 (0 ms)
[ RUN      ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/cortex_a520
[       OK ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/cortex_a520 (0 ms)
[ RUN      ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/cortex_a57
[       OK ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/cortex_a57 (0 ms)
[ RUN      ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/cortex_a65
[       OK ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/cortex_a65 (0 ms)
...
```

Which improves the experience of finding and running this:
```
$ ./unittests/TargetParser/TargetParserTests --gtest_filter=AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/cortex_a65
Note: Google Test filter = AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/cortex_a65
[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from AArch64CPUTests/AArch64CPUTestFixture
[ RUN      ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/cortex_a65
[       OK ] AArch64CPUTests/AArch64CPUTestFixture.testAArch64CPU/cortex_a65 (0 ms)
[----------] 1 test from AArch64CPUTests/AArch64CPUTestFixture (0 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test suite ran. (0 ms total)
[  PASSED  ] 1 test.
```