Art Compiler: fix compiler temps

AOSP CL 78835 "Enable compiler temporaries" built on some earlier
work to enable the compiler to add temps in the style of Dalvik's
vRegs during MIR optimizations.  However, it missed an existing
fixed-size array whose size depended on the number of temps allocated.
The allocation of this array must be delayed until after the
number of compiler temps is known.

The result was array overrun, and strange failures.

Change-Id: I986a3b557e2323e00ba852584de03a02931b3c78