We have now again two functions called h_platform_vasprintf and
h_platform_asprintf. On windows they are implemented in terms of vsnprint
and the like. On BSD/GNU libraries we use the supplied vasprintf and
asprintf.

Since the block of code has been disabled anyway and is not very
portable, we introduce a define to control both the include
and the code.

Storing the size of the blocks is now only activated when DEBUG__MEMFILL
has been defined.

We replace instances of void* w/ char* arithmetics.

This allows system_allocator.c to be compiled with MSVC.

Also we introduce a struct to represent the size_t header.

We use QueryPerformanceCounter which will return realtime, not user
time.

We now have a `stopwatch` to measure time between two moments.

This BSD call will have to be implemented on windows. Right now
we have a stub that just exits the process.

We wrap all remaining references to __attribute__ into a macro call to
H_GCC_ATTRIBUTE, to allow compilation with MSVC CL.EXE

We substitute H_GCC_ATTRIBUTE to any occurence of __attribute__ and
disable its function with non gcc, non clang compilers.

We use a H_ macro so as to not pollute users' namespaces.

On windows build without c4201 so as to allow anonymous struct. This
shows hammer is not C99 compliant but rather C11.