Incorrect errors when __attribute__ is used on enum values in gcc mode

Type: LanguageService

Describe the bug

• OS and Version: Fedora 31
• VS Code Version: 1.41
• C/C++ Extension Version: 0.26.3
• Other extensions you installed (and if the issue persists after disabling them): TBD (how can I disable every extension except for this one? I have 50 extensions installed.)
• A clear and concise description of what the bug is.

There is an identifier exported from GLib, G_PARAM_STATIC_STRINGS (a macro), that is marked as undefined (has red squiggles) even though I can Ctrl+click it to show the definition. Seeing the definition shows no errors. The file that the macro is defined also reports an unusual error though, where an ending } is expected. Not sure if this is throwing off the language server, but something is off.

To Reproduce

repository in question: https://git.sr.ht/~tristan957/harvest-almanac (also mirrored on my GitHub if more convenient)
example of usage: https://git.sr.ht/~tristan957/harvest-almanac/tree/d5ebeb13fb59b3c99e3c43c290b7b7e7aed51020/harvest-glib/harvest-project.c#L334

c_cpp_properties.json

{
    "configurations": [
        {
            "name": "Linux",
            "includePath": [
                "${workspaceFolder}/harvest-glib",
                "/usr/include/gtk-3.0",
                "/usr/include/glib-2.0",
                "/usr/lib64/glib-2.0/include",
                "/usr/include/pango-1.0",
                "/usr/include/cairo",
                "/usr/include/gdk-pixbuf-2.0",
                "/usr/include/atk-1.0",
                "/usr/include/libhandy-0.0",
                "/usr/include/json-glib-1.0",
                "/usr/include/libsoup-2.4",
                "/usr/include/libsecret-1",
                "/usr/include/harfbuzz",
                "/home/tristan957/.local/include",
                "${workspaceFolder}/build/harvest-glib"
            ],
            "defines": [
                "__HARVEST_HEADER_INTERNAL__"
            ],
            "compilerPath": "/usr/bin/gcc",
            "cStandard": "c11",
            "cppStandard": "c++17",
            "intelliSenseMode": "gcc-x64",
            "compileCommands": "${workspaceFolder}/build/compile_commands.json"
        }
    ],
    "version": 4
}

1. Open the repo in VSCode
2. Go to harvest-glib/harvest-project.c line 334, see error on line 335 (any .c file should show the same error fyi)
3. Notice squiggles
4. Ctrl+click (now viewing gparam.h) (https://gitlab.gnome.org/GNOME/glib/blob/master/gobject/gparam.h#L175)
5. Notice error on line 159 of file (https://gitlab.gnome.org/GNOME/glib/blob/master/gobject/gparam.h#L159)
6. Follow the definition of GLIB_DEPRECATED_ENUMERATOR_IN_2_26 to gversionmacros.h and then to gmacros.h
7. See that GLIB_DEPRECATED_ENUMERATOR_IN_2_26 eventually gets defined as __attribute__((__deprecated__))

Expected behavior
Not misreport a defined identifier.

Start with harvest-glib/harvest-project.c around line 334 using the supplied c_cpp_properties.json, then inspect gparam.h around line 159 and follow GLIB_DEPRECATED_ENUMERATOR_IN_2_26 through gversionmacros.h and gmacros.h. Reproduce the diagnostics and verify that the defined G_PARAM_STATIC_STRINGS identifier and the related closing-brace location are no longer reported incorrectly.