BUILD/IMPORT: fix compilation with PLOCK_DISABLE_EBO=1

BUILD/IMPORT: fix compilation with PLOCK_DISABLE_EBO=1

Compilation is broken due to missing __pl_wait_unlock_long() definition
when building with PLOCK_DISABLE_EBO=1. This has been introduced since
the following commit which activates the inlining version of
pl_wait_unlock_long() :
  commit 071d689a514dac522ac3654f53bc22214b5716d0
  MINOR: threads: inline the wait function for pthread_rwlock emulation

Add an extra check on PLOCK_DISABLE_EBO before choosing the inline or
default version of pl_wait_unlock_long() to fix this.