[ASan] Move the shadow range on 32-bit iOS (and iOS Simulator)

to 0x40000000-0x60000000 to avoid address space clash with system libraries.
The solution has been proposed by tahabekireren@gmail.com in https://code.google.com/p/address-sanitizer/issues/detail?id=210
This is also known to fix some Chromium iOS tests.

llvm-svn: 207002