build: Fix NetBSD build issues

* Use LITTLE_ENDIAN instead of __LITTLE_ENDIAN (LITTLE_ENDIAN is what
  POSIX now specifies and everyone seems to define - NetBSD also
  defines _LITTLE_ENDIAN, but not __LITTLE_ENDIAN)

* file descriptors greater than 2 must be explicitly passed to a child
  on NetBSD. POSIX leaves that unspecified, see
  https://pubs.opengroup.org/onlinepubs/9799919799/utilities/V3_chap02.html#exec

* system library functions get declared with visibility "default" on
  NetBSD, so a "hidden" visibility attribute is ignored on a
  redeclaration. Work around by putting the functions in a namespace -
  as they are extern "C", they still end up in the object file without
  the namespace qualifier.

* remove the cast on the NULL pointer on the funopen call - it's not
  needed and the types are different between FreeBSD (fpos_t) and
  NetBSD/OpenBSD (off_t); also trying to change that upstream
  https://github.com/openSUSE/libsolv/pull/603

Change-Id: I6ab7f3c74d18960d7589b403a1c219cdac85a453
Reviewed-on: https://review.haiku-os.org/c/haiku/+/10133
Tested-by: Commit checker robot <[email protected]>
Reviewed-by: Adrien Destugues <[email protected]>

headers/os/support/ByteOrder.h

@@ -30,7 +30,7 @@ typedef enum {
 #define B_SWAP_INT32(arg)    __swap_int32(arg)
 #define B_SWAP_INT16(arg)    __swap_int16(arg)
 
-#if BYTE_ORDER == __LITTLE_ENDIAN
+#if BYTE_ORDER == LITTLE_ENDIAN
 /* Host is little endian */
 
 #define B_HOST_IS_LENDIAN 1

headers/private/fs_shell/fssh_byte_order.h

@@ -37,7 +37,7 @@ typedef enum {
 #define FSSH_B_SWAP_INT32(arg)    __fssh_swap_int32(arg)
 #define FSSH_B_SWAP_INT16(arg)    __fssh_swap_int16(arg)
 
-#if BYTE_ORDER == __LITTLE_ENDIAN
+#if BYTE_ORDER == LITTLE_ENDIAN
 // Host is little endian
 
 #define FSSH_B_HOST_IS_LENDIAN 1