[compiler-rt] [sanitizer_common][PowerPC64] Fix internal_clone() error handling (PR #99908)

[Ilya Leoshkevich via llvm-commits]

================
@@ -1601,8 +1601,8 @@ uptr internal_clone(int (*fn)(void *), void *child_stack, int flags, void *arg,
       "sc\n\t"
 
       /* Test if syscall was successful */
+      "bso-   0f\n\t"
----------------
iii-i wrote:

Right, `cr0.SO` is the primary error indicator. The meaning of `r3` depends on it. On success, `r3=pid`. On error, `r3=errno` (non-negated).

https://github.com/llvm/llvm-project/pull/99908