Reland "[clangd][test] Disable a particular testcase in FindExplicitReferencesTest when LLVM_ENABLE_EXPENSIVE_CHECKS""

The test got re-enabled after d54d71b67e landed.

However it seems that the order is still not deterministic as it
currently passes with -DLLVM_ENABLE_EXPENSIVE_CHECKS=OFF but randomly
fails with expensive checks ON.

clang-tools-extra/clangd/unittests/FindTargetTests.cpp

@@ -823,6 +823,10 @@ TEST_F(FindExplicitReferencesTest, All) {
         "1: targets = {vector}\n"
         "2: targets = {x}\n"},
        // Handle UnresolvedLookupExpr.
+       // FIXME
+       // This case fails when expensive checks are enabled.
+       // Seems like the order of ns1::func and ns2::func isn't defined.
+       #ifndef EXPENSIVE_CHECKS
        {R"cpp(
             namespace ns1 { void func(char*); }
             namespace ns2 { void func(int*); }
@@ -836,6 +840,7 @@ TEST_F(FindExplicitReferencesTest, All) {
         )cpp",
         "0: targets = {ns1::func, ns2::func}\n"
         "1: targets = {t}\n"},
+        #endif
        // Handle UnresolvedMemberExpr.
        {R"cpp(
             struct X {