Fix builds on Mac: icount_ is intptr_t.

Review URL: https://codereview.chromium.org//827453003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42565 260f80e4-7a28-3924-810f-c04153c831b5
Do not clobber dead temp registers at RestoreLiveRegisters as it may destroy the content of the result register as well. Fixes issue 21957.

Review URL: https://codereview.chromium.org//818343002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42566 260f80e4-7a28-3924-810f-c04153c831b5