Reduce memory fragmentation in x86

[bugale]

The method used to allocate trampolines in Detours does not avoid memory fragmentation, which is especially important on platforms where the virtual address space is scarce (like x86).

In this patch we try to minimize the effects of fragmentation by modifying the requested allocation address so that it will be adjacent to the next occupied memory block.

Without this patch, there is a slight chance that in the course of allocating a new trampoline, Detours will undeliberately split a large contiguous memory block into two smaller blocks, thus causing fragmentation.

The effects of fragmentation can be disastrous, since some applications tend to allocate large quantities of memory as part of their start-up code. In case a single block large enough to fulfill the allocation request cannot be found, these applications
will simply fail to start.

Microsoft Reviewers: Open in CodeFlow