Migrate skip checks to --EXTENSIONS--, p3

For rationale, see #6787

Extensions migrated in part 3:
* ftp
* gmp
* iconv
* opcache
* shmop

Add support for replaying warnings in opcache

If opcache.record_warnings is enabled, opcache will record
compilation warnings and replay them when the file is included
again. The pri

Add support for replaying warnings in opcache

If opcache.record_warnings is enabled, opcache will record
compilation warnings and replay them when the file is included
again. The primary use case I have in mind for this is automated
testing of the opcache file cache.

This resolves bug #76535.

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