Allow multiple `TEST_OUTPUT:` sections.

All of them are merged into one automatically in lexical order, and compared with actual output.
Fixes Issue 6057 - Nested enum declaration causes linker errors due to missing sections in obj file.
redo pull #1179
Merge pull request #1512 from 9rnsr/improve_output_test

Allow multiple `TEST_OUTPUT:` sections.
test case output
fix seg fault
Merge pull request #1391 from AndrejMitrovic/Fix6057

Issue 6057 - Nested enum declaration causes linker errors
Merge pull request #1526 from WalterBright/b23

Redo of pull #1179