Fix logic to detect cl::option equality. (#65754)

This is a new attempt of https://reviews.llvm.org/D159481, this time as
GitHub PR.

`GenericOptionValue::compare()` should return `true` for a match.

- `OptionValueBase::compare()` always returns `false` and shouldn't
match anything.
- `OptionValueCopy::compare()` returns `false` if not `Valid` which
corresponds to no match.

Also adding some tests.

1 files changed, 2 insertions, 2 deletions

diff --git a/llvm/lib/Support/CommandLine.cpp b/llvm/lib/Support/CommandLine.cpp
index d3efb8b..55633d7 100644
--- a/llvm/lib/Support/CommandLine.cpp
+++ b/llvm/lib/Support/CommandLine.cpp
@@ -2181,7 +2181,7 @@ void generic_parser_base::printGenericOptionDiff(
 
   unsigned NumOpts = getNumOptions();
   for (unsigned i = 0; i != NumOpts; ++i) {
-    if (Value.compare(getOptionValue(i)))
+    if (!Value.compare(getOptionValue(i)))
       continue;
 
     outs() << "= " << getOption(i);
@@ -2189,7 +2189,7 @@ void generic_parser_base::printGenericOptionDiff(
     size_t NumSpaces = MaxOptWidth > L ? MaxOptWidth - L : 0;
     outs().indent(NumSpaces) << " (default: ";
     for (unsigned j = 0; j != NumOpts; ++j) {
-      if (Default.compare(getOptionValue(j)))
+      if (!Default.compare(getOptionValue(j)))
         continue;
       outs() << getOption(j);
       break;