asan: Use `#if` to test CAN_SANITIZE_LEAKS

[mcgrathr]

Summary

The if (0) isn't necessarily optimized out so as not to create
a link-time reference to LSan runtime functions that might not
exist. So use explicit conditional compilation instead.

[mcgrathr]

fix comment typo in earlier change

[phosek]

LGTM

[kcc]

a drive-by comment -- I would really appreciate *not* adding any new uses of C preprocessor.

compiler-rt/lib/asan/asan_rtl.cpp

#endif
   InitTlsSize();
 
   // Create main thread.
   AsanThread *main_thread = CreateMainThread();
   CHECK_EQ(0, main_thread->tid());
   force_interface_symbols();  // no-op.
   SanitizerInitializeUnwinder();
 
-  if (CAN_SANITIZE_LEAKS) {
-    __lsan::InitCommonLsan();
-    InstallAtExitCheckLeaks();
-  }
+#if CAN_SANITIZE_LEAKS
+#endif
 
 #if CAN_SANITIZE_UB
   __ubsan::InitAsPlugin();
 #endif
 
   InitializeSuppressions();
 
   if (CAN_SANITIZE_LEAKS) {

compiler-rt/lib/lsan/lsan_common_fuchsia.cpp

 // Nothing to do here.
 void ProcessPlatformSpecificAllocations(Frontier *frontier) {}
 
 // On Fuchsia, we can intercept _Exit gracefully, and return a failing exit
 // code if required at that point.  Calling Die() here is undefined
 // behavior and causes rare race conditions.
 void HandleLeaks() {}
 
-// This is defined differently in asan_fuchsiap.cpp and lsan_fuchsia.cpp.
+// This is defined differently in asan_fuchsia.cpp and lsan_fuchsia.cpp.
 bool UseExitcodeOnLeak();
 
 int ExitHook(int status) {
   if (common_flags()->detect_leaks && common_flags()->leak_check_at_exit) {
     if (UseExitcodeOnLeak())
       DoLeakCheck();
     else
       DoRecoverableLeakCheckVoid();