scudo: Update TLS_SLOT_SANITIZER value.

[pcc]

Summary

Android now allocates only 8 fixed TLS slots. Somehow we were getting away
with using a non-existent slot until now, but in some cases the TLS slots
were being placed at the end of a page, which led to a segfault at startup.

[eugenis]

LGTM

compiler-rt/lib/scudo/standalone/linux.h

#define __get_tls()                                                            \
   })
 #else
 #error "Unsupported architecture."
 #endif
 
 // The Android Bionic team has allocated a TLS slot for sanitizers starting
 // with Q, given that Android currently doesn't support ELF TLS. It is used to
 // store sanitizer thread specific data.
-static const int TLS_SLOT_SANITIZER = 8; // TODO(kostyak): 6 for Q!!
+static const int TLS_SLOT_SANITIZER = 6;
 
 ALWAYS_INLINE uptr *getAndroidTlsPtr() {
   return reinterpret_cast<uptr *>(&__get_tls()[TLS_SLOT_SANITIZER]);
 }
 
 #endif // SCUDO_ANDROID
 
 } // namespace scudo
 
 #endif // SCUDO_LINUX
 
 #endif // SCUDO_LINUX_H_