Add a mmap flag (MAP_32BIT) on 64-bit platforms

to request that a mapping use an address in the first 2GB of the
process's address space. This flag should have the same semantics as the
same flag on Linux.

To facilitate this, add a new parameter to vm_map_find() that specifies an
optional maximum virtual address.  While here, fix several callers of
vm_map_find() to use a VMFS_* constant for the findspace argument instead of
TRUE and FALSE.

Reviewed by:	alc
Approved by:	re (kib)

newlib/libc/sys/rtems/include/sys/mman.h

@@ -91,6 +91,9 @@
  */
 #define	MAP_NOCORE	 0x00020000 /* dont include these pages in a coredump */
 #define	MAP_PREFAULT_READ 0x00040000 /* prefault mapping for reading */
+#ifdef __LP64__
+#define	MAP_32BIT	 0x00080000 /* map in the low 2GB of address space */
+#endif
 
 /*
  * Request specific alignment (n == log2 of the desired alignment).