move __BYTE_ORDER definition to alltypes.h

this change is motivated by the intersection of several factors.
presently, despite being a nonstandard header, endian.h is exposing
the unprefixed byte order macros and functions only if _BSD_SOURCE or
_GNU_SOURCE is defined. this is to accommodate use of endian.h from
other headers, including bits headers, which need to define structure
layout in terms of endianness. with time64 switch-over, even more
headers will need to do this.

at the same time, the resolution of Austin Group issue 162 makes
endian.h a standard header for POSIX-future, requiring that it expose
the unprefixed macros and the functions even in standards-conforming
profiles. changes to meet this new requirement would break existing
internal usage of endian.h by causing it to violate namespace where
it's used.

instead, have the arch's alltypes.h define __BYTE_ORDER, either as a
fixed constant or depending on the right arch-specific predefined
macros for determining endianness. explicit literals 1234 and 4321 are
used instead of __LITTLE_ENDIAN and __BIG_ENDIAN so that there's no
danger of getting the wrong result if a macro is undefined and
implicitly evaluates to 0 at the preprocessor level.

the powerpc (32-bit) bits/endian.h being removed had logic for varying
endianness, but our powerpc arch has never supported that and has
always been big-endian-only. this logic is not carried over to the new
__BYTE_ORDER definition in alltypes.h.

2 files changed, 4 insertions, 7 deletions

diff --git a/include/alltypes.h.in b/include/alltypes.h.in
index 8e76c839..1ab40395 100644
--- a/include/alltypes.h.in
+++ b/include/alltypes.h.in
@@ -1,3 +1,6 @@
+#define __LITTLE_ENDIAN 1234
+#define __BIG_ENDIAN 4321
+
 TYPEDEF unsigned _Addr size_t;
 TYPEDEF unsigned _Addr uintptr_t;
 TYPEDEF _Addr ptrdiff_t;
diff --git a/include/endian.h b/include/endian.h
index 1bd44451..2c2ad5f4 100644
--- a/include/endian.h
+++ b/include/endian.h
@@ -3,15 +3,9 @@
 
 #include <features.h>
 
-#define __LITTLE_ENDIAN 1234
-#define __BIG_ENDIAN 4321
 #define __PDP_ENDIAN 3412
 
-#if defined(__GNUC__) && defined(__BYTE_ORDER__)
-#define __BYTE_ORDER __BYTE_ORDER__
-#else
-#include <bits/endian.h>
-#endif
+#include <bits/alltypes.h>
 
 #if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)