[tsan] Respect !nosanitize metadata and remove gcov special case

Certain instrumentations set the !nosanitize metadata for inserted
instructions, which are generally not interested for sanitizers. Skip
tsan instrumentation like we do for asan (D126294)/msan/hwasan.

-fprofile-arcs instrumentation has data race unless
-fprofile-update=atomic is specified. Let's remove the the `__llvm_gcov`
special case from commit 0222adbc (2016)
as the racy instructions have the !nosanitize metadata.
(-fprofile-arcs instrumentation does not use `__llvm_gcda` as global variables.)

```
std::atomic<int> c;
void foo() { c++; }
int main() {
  std::thread th(foo);
  c++;
  th.join();
}
```
Tested that `clang++ --coverage -fsanitize=thread a.cc && ./a.out` does
not report spurious tsan errors.

Also remove the default CC1 option -fprofile-update=atomic for
-fsanitize=thread to make options more orthogonal.

Reviewed By: Enna1

Differential Revision: https://reviews.llvm.org/D158385