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
getpagesize on Linux returns an int. Fix QEMU's implementation for
Windows to return an int (instead of size_t), too.
This fixes a compiler warning which was introduced recently
(commit 093e3c42).
Backports commit a28c2f2df7679e3a87789e9fb7ed69331f697297 from qemu
