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: SixWeining, xen0n, MaskRay, DavidSpickett
Differential Revision: https://reviews.llvm.org/D137312
case llvm::Triple::ppc64le:
case llvm::Triple::x86_64:
case llvm::Triple::riscv64:
+ case llvm::Triple::loongarch64:
arch_64.SetTriple(triple);
arch_32.SetTriple(triple.get32BitArchVariant());
break;