build on clang/musl fails with:
```
FEX/unittests/APITests/Allocator.cpp:17:5: error: use of undeclared identifier 'close'
FEX/unittests/APITests/Allocator.cpp:23:5: error: use of undeclared identifier 'lseek'; did you mean 'fseek'?
FEX/unittests/APITests/Allocator.cpp:23:11: error: cannot initialize a parameter of type 'FILE *' (aka 'struct _IO_FILE *') with an lvalue of type 'int'
FEX/unittests/APITests/Allocator.cpp:24:5: error: use of undeclared identifier 'write'; did you mean '_IO_cookie_io_functions_t::write'?
FEX/unittests/APITests/Allocator.cpp:24:5: error: invalid use of non-static data member 'write'
```
include header to provide defintions
fix: #5476
Signed-off-by: Pepper Gray <hello@peppergray.xyz>
This function can be unit-tested more easily, and the stack special is more
cleanly handled as a post-collection step.
There is a minor functional change: The stack special case didn't trigger
previously if the range end was within the stack mapping. This is now fixed.
Pepper Gray