[sanitizer] GetTls: Work around Ubuntu 16.04 broken glibc

[MaskRay]

Summary

I hope that we can collect more information, even if we want to add the workaround.
This blocks TLS clean-ups.

compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp

#elif SANITIZER_LINUX
   uptr align;
   GetStaticTlsRange(addr, size, &align);
 #if defined(__x86_64__) || defined(__i386__) || defined(__s390__)
   if (SANITIZER_GLIBC) {
 #if defined(__s390__)
     align = Max<uptr>(align, 16);
 #else
     align = Max<uptr>(align, 64);
+    // Work around a broken glibc on Ubuntu 16.04 amd64.
+    if (*addr == 0 && sizeof(void *) == 8) {
+      void *ptr = dlsym(RTLD_NEXT, "_dl_get_tls_static_info");
+      size_t tls_align;
+      uptr addr2;
+      ((void (*)(uptr *, size_t *))ptr)(size, &tls_align);
+      asm("mov %%fs:0,%0" : "=r"(addr2));
+      *addr = addr2 + ThreadDescriptorSize() - *size;
+      return;
+    }
 #endif
   }
   const uptr tp = RoundUpTo(*addr + *size, align);
 
   // lsan requires the range to additionally cover the static TLS surplus
   // (elf/dl-tls.c defines 1664). Otherwise there may be false positives for
   // allocations only referenced by tls in dynamically loaded modules.
   if (SANITIZER_GLIBC)