score: Update due to API changes
libtests/gxx01: Avoid random memory read/write
rtems: Create semaphore implementation header

Move implementation specific parts of sem.h and sem.inl into new header
file semimpl.h.  The sem.h contains now only the application visible
API.
posix: Create mutex implementation header

Move implementation specific parts of mutex.h and mutex.inl into new
header file muteximpl.h.  The mutex.h contains now only the application
visible API.
score: Create mutex implementation header

Move implementation specific parts of coremutex.h and coremutex.inl into
new header file coremuteximpl.h.  The coremutex.h contains now only the
application visible API.
rtems: Convert to inline functions
posix: Convert to inline function
score: Convert to inline function
score: Avoid direct usage of _Thread_Executing

Pass the executing thread as a function parameter.  Obtain the executing
thread inside a thread dispatch critical section to avoid problems on
SMP.
rtems, posix: Use _Thread_Get_executing()
libcsupport: Do not use _ISR_Nest_level

The _Thread_Dispatch_is_enabled() is false if _ISR_Nest_level is not
equal to zero.