[LLDB] [LoongArch] Add loongarch64 case in ComputeHostArchitectureSupport()

This is a simple change, loongarch64 host also supports 32-bit binaries,
so note it.

Without this patch:

```
[loongson@linux build]$ ./tools/lldb/unittests/Host/HostTests | tail -6
[==========] 78 tests from 18 test suites ran. (16 ms total)
[  PASSED  ] 77 tests.
[  FAILED  ] 1 test, listed below:
[  FAILED  ] HostTest.GetProcessInfo

 1 FAILED TEST
```

With this patch:

```
[loongson@linux build]$ ./tools/lldb/unittests/Host/HostTests | tail -2
[==========] 78 tests from 18 test suites ran. (15 ms total)
[  PASSED  ] 78 tests.
```

Reviewed By: xen0n, MaskRay, DavidSpickett

Differential Revision: https://reviews.llvm.org/D137312