[lldb] Disable auto fix-its when evaluating expressions in the test suite

Summary:
Currently the test suite runs with enabled automatically applied Clang fix-its for expressions.
This is causing that sometimes incorrect expressions in tests are still evaluated even though they
are actually incorrect. Let's disable this feature in the test suite so that we know when expressions
are wrong and leave the fix-it testing to the dedicated tests for that feature.

Also updates the `lang/cpp/operators/` test as it seems Clang needs the `struct` keywords
before C and would otherwise fail without fixits.

Reviewers: jingham, JDevlieghere, shafik

Reviewed By: JDevlieghere, shafik

Subscribers: shafik, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D74957