[9] RFR (L): 8015774: Add support for multiple code heaps

[Andrew Haley]

This has some potential impact on AArch64.

The issue there is that branch instructions have a range of +- 128Mb.
Any further than that and you have to use multiple instructions, and
then you have problems with thread-safe patching.

So, is it possible to allocate all of the code heaps in a single
block, so that we won't exceed that range?

Andrew.