Make `spl_autoload_functions()` return the same as PHP

Summary: This fixes Callable format: Class::method isconsist with PHP

Closes #3700
Closes https://github.com/facebook/hhvm/pull/3776

Reviewed By: @fredemmott

Differential Revision: D1563676
Don't use system SQLite if headers not found.

Summary: Gentoo multilib environments may have situations when there is no 64-bit SQLite package installed but filesystem containts 32-bit libsqlite3.so and we have `LIBSQLITE3_LIBRARY` set, but not `LIBSQLITE3_INCLUDE_DIR` and `LIBSQLITE3_FOUND`. Don't try to use system SQLite headers if they are not present.

Fixes #3108.
Closes https://github.com/facebook/hhvm/pull/3774

Reviewed By: @fredemmott

Differential Revision: D1560875
Remove unused StringData::MakeMalloced and StringData::destruct()

Summary: These look to have been removed previously when moving to APCHandle.

Reviewed By: @markw65

Differential Revision: D1563581