Fix full code generator to not use --debug-code if it is in

Fix full code generator to not use --debug-code if it is in
mksnapshot or a VM that is booted from a snapshot.  --debug-code
can still have an effect on stub and optimized code and it still
works on the full code generator when running without snapshots.

The deoptimizer generates full-code-generator code and relies on it having
the same layout as last time.  This means that the code the full code
generator makes for the snapshot should be the same as the code it makes
later.  This change makes the full code generator create more consistent
code between mksnapshot time and run time.

This is a bug fix and a step towards making the snapshot code more robust.
Committed: https://code.google.com/p/v8/source/detail?r=12239

[Jakob Kummerow, 2012-07-31 14:44:58]

LGTM with a nit.

https://chromiumcodereview.appspot.com/10834085/diff/1/src/x64/assembler-x64.cc
File src/x64/assembler-x64.cc (right):

https://chromiumcodereview.appspot.com/10834085/diff/1/src/x64/assembler-x64....
src/x64/assembler-x64.cc:1238: if (is_int8(offs - short_size) &&
!predictable_code_size_) {
A comment would be nice about why we have to disable automatic near jumps on
x64. Draft based on our offline discussion:
// On x64, when code is recompiled for debugging, some places need to be padded
// out to a certain size. The debugger is keeping track of how often it did
// this, but if the size of jump instructions can also change, that's not
// enough and the calculated offsets would be incorrect.