Load jit compiler pre zygote fork

Reduces PSS for libart-compiler.so from 115KB to 2KB per app.

Also some clean-up.

Bug: 27810774

(cherry picked from commit ff2376770c1c6d301778c41e5c27c808a38e6968)

Change-Id: Ic0077a07c21ed9f1952a6c29863a5c0e5bacc01a
3 files changed