Speed up the GenerateExportHeader unit test (#14453).

Instead of running many small tests with many cmake projects, simply
compare the generated export header against a reference.
Merge topic 'GenerateExportHeader-tests' into next

0f9e5de Speed up the GenerateExportHeader unit test (#14453).
Remove obsolete
Merge some GenerateExportHeader subtests.
Merge topic 'GenerateExportHeader-tests' into next

50a50ae Merge some GenerateExportHeader subtests.
b52d6c7 Remove obsolete
Speed up the GenerateExportHeader unit test (#14453).

Instead of running many small tests with many cmake projects, simply
compare the generated export header against a reference.

Remove the helper macros and the try_compiles which are duplicates
of the library build tests.
Merge some GenerateExportHeader subtests.
Merge topic 'GenerateExportHeader-tests' into next

2410b91 Merge some GenerateExportHeader subtests.
4017db1 Speed up the GenerateExportHeader unit test (#14453).