[LLDB][ProcessGDBRemote] Put SetCanJIT behind a guard clause

Summary:
In D73806555, I have `SetCanJIT` be modified if the process can be resumed. This caused some test failures because the process couldn't Jit!

After some investigation, I originally tried putting this behind `CanJIT() && !non_resumable`, but that itself would modify the state of Process. So I've settled on 'if we're in a non resumable stop, now disable JIT'. This will unblock the release and I will CP back to rc-main.

Test Plan:
```
./bin/llvm-lit -sv /data/users/jalalonde/llvm-sand/external/llvm-project/lldb/test/API/functionalities/thread/thread_specific_break_plus_condition/TestThreadSpecificBpPlusCondition.py

Testing Time: 34.21s

Total Discovered Tests: 1
  Passed: 1 (100.00%)
```

Reviewers: gclayton, peix

Reviewed By: gclayton, peix

Subscribers: #lldb_team

Differential Revision: https://phabricator.intern.facebook.com/D75004779

Author: Jlalond

lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp

@@ -967,10 +967,16 @@ void ProcessGDBRemote::DidLaunchOrAttach(ArchSpec &process_arch) {
       GetTarget().SetArchitecture(process_arch);
     }
 
-    // If the process is in a non resumable stop, we'll keep erroring out
-    // trying to jit and continue the process. So we set can JIT to false
-    // so any expression is evaluated in LLDB.
-    SetCanJIT(m_gdb_comm.SafeToResume());
+    // We don't want to cause side-effects unintentionally on the happy path
+    // so we don't touch CanJIT unless we know we've hit a non-resumable
+    // state. Additionally we don't check `CanJIT` because it itself
+    // would modify the state of CanJIT.
+    if (!m_gdb_comm.SafeToResume()) {
+      // If the process is in a non resumable stop, we'll keep erroring out
+      // trying to jit and continue the process. So we set can JIT to false
+      // so any expression is evaluated in LLDB.
+      SetCanJIT(false);
+    }
   }
 
   // Target and Process are reasonably initailized;