[Support] Support NetBSD PaX MPROTECT in sys::Memory.

Removes AllocateRWX, setWritable and setExecutable from sys::Memory and
standardizes on allocateMappedMemory / protectMappedMemory. The
allocateMappedMemory method is updated to request full permissions for memory
blocks so that they can be marked executable later.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@318464 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed