Optimize performance schema likely/unlikely

Performance schema likely/unlikely assume that performance schema
is enabled by default, which causes a performance degradation for
default installations that doesn't have performance schema enabled.

Fixed by changing the likely/unlikely in PS to assume it's
not enabled. This can be changed by compiling with
-DPSI_ON_BY_DEFAULT

Other changes:
- Added psi_likely/psi_unlikely that is depending on
  PSI_ON_BY_DEFAULT. psi_likely() is assumed to be true
  if PS is enabled.
- Added likely/unlikely to some PS interface code.
- Moved pfs_enabled to mysys (was initialized but not used before)
- Added "if (pfs_likely(pfs_enabled))" around calls to PS to avoid
  an extra call if PS is not enabled.
- Moved checking flag_global_instrumention before other flags
  to speed up the case when PS is not enabled.

include/mysql/psi/mysql_table.h

@@ -87,7 +87,7 @@
 #ifdef HAVE_PSI_TABLE_INTERFACE
   #define MYSQL_TABLE_IO_WAIT(PSI, OP, INDEX, FLAGS, PAYLOAD) \
     {                                                         \
-      if (PSI != NULL)                                        \
+      if (psi_likely(PSI != NULL))                            \
       {                                                       \
         PSI_table_locker *locker;                             \
         PSI_table_locker_state state;                         \
@@ -120,7 +120,7 @@
 #ifdef HAVE_PSI_TABLE_INTERFACE
   #define MYSQL_TABLE_LOCK_WAIT(PSI, OP, FLAGS, PAYLOAD) \
     {                                                    \
-      if (PSI != NULL)                                   \
+      if (psi_likely(PSI != NULL))                       \
       {                                                  \
         PSI_table_locker *locker;                        \
         PSI_table_locker_state state;                    \
@@ -186,7 +186,7 @@ inline_mysql_start_table_lock_wait(PSI_table_locker_state *state,
                                    enum PSI_table_lock_operation op,
                                    ulong flags, const char *src_file, uint src_line)
 {
-  if (psi != NULL)
+  if (psi_likely(psi != NULL))
   {
     struct PSI_table_locker *locker;
     locker= PSI_TABLE_CALL(start_table_lock_wait)
@@ -203,7 +203,7 @@ inline_mysql_start_table_lock_wait(PSI_table_locker_state *state,
 static inline void
 inline_mysql_end_table_lock_wait(struct PSI_table_locker *locker)
 {
-  if (locker != NULL)
+  if (psi_likely(locker != NULL))
     PSI_TABLE_CALL(end_table_lock_wait)(locker);
 }
 #endif