Compiler leak

Fix a memory leak in the Smalltalk compiler

There are too much INC_SAVE_POINTER/INC_RESTORE_POINTER in the compiler
(compile_block and _gst_make_constant) the objects created in those
functions can be GCed (during an allocation) because they are no more
protected. Removing the exta INC_SAVE_POINTER/INC_RESTORE_POINTER is safe
because the root compiler functions have them.