[ubsan_minimal] Build on Solaris (#184976)

Two tests currently `FAIL` on Solaris/amd64 and Solaris/sparcv9:

```
  SafeStack-Standalone-i386 :: overflow.c
  SafeStack-Standalone-x86_64 :: overflow.c
```

This happens because `libclang_rt.ubsan_minimal.a` isn't built on
Solaris although it's required with `-fsanitize-minimal-runtime`.

This patch fixes this.

Tested on `amd64-pc-solaris2.11` and `sparcv9-sun-solaris2.11`.

NOKEYCHECK=True
GitOrigin-RevId: d6b33bda134f933f5ec1b7a948441ab4e98bbb8d