[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`.
