Changes

Made PreprocessorMacro and TokenList public (#676)

### Changes

With this PR, `PreprocessorMacro` and its subclasses are no longer package-private but public instead. Same goes for `TokenList`.

### Reasons for the changes

When parsing C/C++ code with CDT as a standalone library I want to track certain macro expansions using the [MacroExpander](https://github.com/eclipse-cdt/cdt/blob/main/core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/parser/scanner/MacroExpander.java).

It is not actually part of the public API but declared as `public`. It takes an argument `macroDictionary` of type `CharArrayMap<PreprocessorMacro>` in its constructor. Currently, `PreprocessorMacro` is package-privat and thus, not available without shadowing (i.e., implementing my custom macro tracker in the package `org.eclipse.cdt.internal.core.parser.scanner`).

It questionable whether it is a good design decision to have public and private API mixed together here (rendering the usage of the constructor of `MacroExpander` impossible).

Also, another problem occurs once you take the route of shadowing to have access to `PreprocessorMacro`: the CDT jars are all signed during release (makes sense) but, sadly speaking, that will result in a `SecurityException` when trying to call their API from your own (unsigned) code which lives in the shadowed package (in my case in `org.eclipse.cdt.internal.core.parser.scanner`).

### Problem solved

MacroExpander can now be used from the outside because `PreprocessorMacro` and `TokenList` are no longer package-private. Shadowing is no longer needed. Signed jars are no longer a problem.

Invoke "gcc" to build assembler files

Enables pre-processing of *.S and *.sx source files.

Enhance legacy GNU assembler flag detection

Workaround #684 by disabling dsf-gdb tests (#685)

This only disables running the tests on Jenkins as the GitHub actions
these tests work fine for now.

See https://github.com/eclipse-cdt/cdt/issues/684