AND PFS COMPILED OUT

Before this fix, when building a server without the performance schema,
commands like SHOW STATUS would fail with errors like:

mysql> show status;
ERROR 1146 (42S02): Table 'performance_schema.session_status' doesn't exist

The reason for the error is that SHOW STATUS is rewritten internally
as a SELECT ... FROM performance_schema.session_status,
which fails when the performance schema storage engine is missing.

In MySQL 5.7, compiling without the performance schema is no longer
supported, because tables like:
- table performance_schema.host_cache
- the replication tables performance_schema.replication_*
- the status tables like performance_schema.session_status
- the system variables tables like performance_schema.session_variables
are exposed, which rely on the performance schema -- storage engine --,
even when the performance schema -- instrumentation -- is not used.

With this fix, the performance schema storage engine itself is now mandatory.

Compiling:
- the storage engine
- the various instrumentation calls
is now decoupled, as the former is needed independently of the later.

To build a server without the -- instrumentation --,
which is the main motivation to build without the performance schema in
general, the following cmake options can be used instead of
option -DWITH_PERFSCHEMA_STORAGE_ENGINE=0
- DISABLE_PSI_THREAD
- DISABLE_PSI_MUTEX
- DISABLE_PSI_RWLOCK
- DISABLE_PSI_COND
- DISABLE_PSI_FILE
- DISABLE_PSI_TABLE
- DISABLE_PSI_SOCKET
- DISABLE_PSI_STAGE
- DISABLE_PSI_STATEMENT
- DISABLE_PSI_SP
- DISABLE_PSI_PS
- DISABLE_PSI_IDLE
- DISABLE_PSI_STATEMENT_DIGEST
- DISABLE_PSI_METADATA
- DISABLE_PSI_MEMORY
- DISABLE_PSI_TRANSACTION