Fix unused-return in folly/debugging/symbolizer/DwarfUtil.cpp +4

Summary:
LLVM has a warning `-Wunreachable-code-return` which identifies return statements that cannot be reached.

In innocuous situations such statements are often present:
* to satisfy a compiler warning that existed before `[[noreturn]]` was introduced. Now that we have `[[noreturn]]`, this use is not necessary.
* to specify a return type. But there are clearer ways to do this.
* in place of the more legible `__builtin_unreachable()` (which will soon become `std::unreachable()`). In this case, we should use the more legible alternative.
* because the programmer was afraid of the function unexpectedly returning. But we check for this condition with `-Wreturn-type`.

In dangerous situations such statements can obscure the intended execution of the program or even hide an erroneous early return.

In this diff, we remove one or more unreachable returns.

 - If you approve of this diff, please use the "Accept & Ship" button :-)

Differential Revision: D77424526

fbshipit-source-id: b21cc6d31e70344cb2b21dea194d6685327adecf

Author: r-barnes

third-party/folly/src/folly/debugging/symbolizer/DwarfUtil.cpp

@@ -761,7 +761,6 @@ Attribute readAttribute(
       FOLLY_SAFE_DFATAL("invalid attribute form: ", spec.form);
       return {spec, die, 0u};
   }
-  return {spec, die, 0u};
 }
 
 /*

third-party/folly/src/folly/debugging/symbolizer/detail/Debug.cpp

@@ -78,8 +78,9 @@ static r_debug* r_debug_cache_;
 struct r_debug* get_r_debug() {
 #if FOLLY_DETAIL_HAS_R_DEBUG
   return r_debug_cache_;
-#endif
+#else
   return nullptr;
+#endif
 }
 
 } // namespace detail