Use BLOCK_ENTRY_PC in place of most uses of BLOCK_START
This change/patch substitues BLOCK_ENTRY_PC for BLOCK_START in
places where BLOCK_START is used to obtain the address at which
execution should enter the block. Since blocks can now contain
non-contiguous ranges, the BLOCK_START - which is still be the
very lowest address in the block - might not be the same as
BLOCK_ENTRY_PC.
There is a change to infrun.c which is less obvious and less mechanical.
I'm posting it as a separate patch.