Reuse ZoneList memory if possible.

Clear() is rather wasteful for ZoneLists, because it discards
all previously allocated memory, making it impossible to reuse
until the whole Zone is released. Better use Rewind(0) in this
case, which just resets the length to zero.

R=jarin@chromium.org

Review URL: https://codereview.chromium.org/302783007

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21545 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Extract build configuration into a separate header and move it to the base lib

With this, change, atomicops, once, and lazy instance are no longer dependant
on v8 core. I'll move them in a follow-up change to the libbase as well.

BUG=none
R=jkummerow@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/303463005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21546 ce2b1a6d-e550-0410-aec6-3dcde31c8c00