Fix compiler issue with mmap_internal

Compiling mmap_internal fails to compile when we use -1 for MMAP2_PAGE_UNIT
on 32 bit architectures.  The error is as follows:

    ../sysdeps/unix/sysv/linux/mmap_internal.h:30:8: error: unknown type
    name 'uint64_t'
    |
       30 | static uint64_t page_unit;
	  |
	  |        ^~~~~~~~

Fix by adding including stdint.h.