[lldb] NFC: refactor CompileUnit::ResolveSymbolContext

Summary:
I found the above named method hard to read because it had

a) many nested blocks and
b) one return statement at the end with some logic involved.

I decided to refactor this function by employing an early exit strategy.
In order to capture the logic in the return statement and to not have it
repeated more than once I chose to implement a very small lamda function
that captures all the variables it needs.

This is a non-functional change (NFC).

Reviewers: jdoerfert

Subscribers: lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D70774

lldb/source/API/SBThread.cpp

@@ -914,9 +914,10 @@ SBError SBThread::StepOverUntil(lldb::SBFrame &sb_frame,
     const bool exact = false;
 
     SymbolContextList sc_list;
-    const uint32_t num_matches = frame_sc.comp_unit->ResolveSymbolContext(
-        step_file_spec, line, check_inlines, exact, eSymbolContextLineEntry,
-        sc_list);
+    frame_sc.comp_unit->ResolveSymbolContext(step_file_spec, line,
+                                             check_inlines, exact,
+                                             eSymbolContextLineEntry, sc_list);
+    const uint32_t num_matches = sc_list.GetSize();
     if (num_matches > 0) {
       SymbolContext sc;
       for (uint32_t i = 0; i < num_matches; ++i) {