[clangd] Make USRs for macros to be position independent

[kadircet]

Summary

USRs for macros were not cannonical due to usage of cursor location
instead of definition location.

[jkorous]

Thanks for fixing this Kadir!

LGTM

clangd/XRefs.cpp

for (const auto &Sym : Symbols.Decls) {
     }
     Results.push_back(std::move(NewSymbol));
   }
 
   for (const auto &Macro : Symbols.Macros) {
     SymbolDetails NewMacro;
     NewMacro.name = Macro.Name;
     llvm::SmallString<32> USR;
-    if (!index::generateUSRForMacro(NewMacro.name, Loc, SM, USR)) {
+    if (!index::generateUSRForMacro(NewMacro.name,
+                                    Macro.Info->getDefinitionLoc(), SM, USR)) {
       NewMacro.USR = USR.str();
       NewMacro.ID = SymbolID(NewMacro.USR);
     }
     Results.push_back(std::move(NewMacro));
   }
 
   return Results;
 }
 
 } // namespace clangd
 } // namespace clang

unittests/clangd/SymbolInfoTests.cpp

std::pair<const char *, std::vector<SymbolDetails>>
           };
         )cpp",
               {CreateExpectedSymbolDetails("ii", "", "c:@ii")}},
           {
               R"cpp( // Macro reference
           #define MACRO 5\nint i = MAC^RO;
         )cpp",
               {CreateExpectedSymbolDetails("MACRO", "",
-                                           "c:TestTU.cpp@55@macro@MACRO")}},
+                                           "c:TestTU.cpp@38@macro@MACRO")}},
+          {
+              R"cpp( // Macro reference
+          #define MACRO 5\nint i = MACRO^;
+        )cpp",
+              {CreateExpectedSymbolDetails("MACRO", "",
+                                           "c:TestTU.cpp@38@macro@MACRO")}},
           {
               R"cpp( // Multiple symbols returned - using overloaded function name
           void foo() {}
           void foo(bool) {}
           void foo(int) {}
           namespace bar {
             using ::fo^o;
           }