Clean up includes so that osdep.h is included first and headers
which it implies are not included manually.
This commit was created with scripts/clean-includes.
Backports commit aafd758410015e08b1aa8964d739ba8587ce58dc from qemu
Anonymous and file-backed RAM allocation are now almost exactly the same.
Reduce code duplication by moving RAM mmap code out of oslib-posix.c and
exec.c.
Backports commit 794e8f301a17953efa78ab7538019ec43c59e82a from qemu