[OpenMP] fix endianness dependent definitions in OMP headers for MSVC (llvm#84540)

MSVC does not define __BYTE_ORDER__ making the check for BigEndian
erroneously evaluate to true and breaking the struct definitions in MSVC
compiled builds correspondingly. The fix adds an additional check for
whether __BYTE_ORDER__ is defined by the compiler to fix these.

---------

Co-authored-by: Vadim Paretsky <b-vadipa@microsoft.com>
(cherry picked from commit 110141b)

Author: vadikp-intel

openmp/runtime/src/kmp.h

@@ -2506,7 +2506,7 @@ typedef struct kmp_depend_info {
   union {
     kmp_uint8 flag; // flag as an unsigned char
     struct { // flag as a set of 8 bits
-#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+#if defined(__BYTE_ORDER__) && (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)
       /* Same fields as in the #else branch, but in reverse order */
       unsigned all : 1;
       unsigned unused : 3;
@@ -2671,7 +2671,7 @@ typedef struct kmp_task_stack {
 #endif // BUILD_TIED_TASK_STACK
 
 typedef struct kmp_tasking_flags { /* Total struct must be exactly 32 bits */
-#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+#if defined(__BYTE_ORDER__) && (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)
   /* Same fields as in the #else branch, but in reverse order */
 #if OMPX_TASKGRAPH
   unsigned reserved31 : 6;

openmp/runtime/src/kmp_lock.h

@@ -120,7 +120,8 @@ extern void __kmp_validate_locks(void);
 
 struct kmp_base_tas_lock {
   // KMP_LOCK_FREE(tas) => unlocked; locked: (gtid+1) of owning thread
-#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__ && __LP64__
+#if defined(__BYTE_ORDER__) && (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__) &&     \
+    __LP64__
   // Flip the ordering of the high and low 32-bit member to be consistent
   // with the memory layout of the address in 64-bit big-endian.
   kmp_int32 depth_locked; // depth locked, for nested locks only

openmp/runtime/test/tasking/bug_nested_proxy_task.c

@@ -50,7 +50,7 @@ typedef struct kmp_depend_info {
      union {
         kmp_uint8 flag; // flag as an unsigned char
         struct { // flag as a set of 8 bits
-#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+#if defined(__BYTE_ORDER__) && (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)
           unsigned all : 1;
           unsigned unused : 3;
           unsigned set : 1;

openmp/runtime/test/tasking/bug_proxy_task_dep_waiting.c

@@ -47,7 +47,7 @@ typedef struct kmp_depend_info {
      union {
         kmp_uint8 flag; // flag as an unsigned char
         struct { // flag as a set of 8 bits
-#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+#if defined(__BYTE_ORDER__) && (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)
           unsigned all : 1;
           unsigned unused : 3;
           unsigned set : 1;

openmp/runtime/test/tasking/hidden_helper_task/common.h

@@ -17,7 +17,7 @@ typedef struct kmp_depend_info {
   union {
     unsigned char flag;
     struct {
-#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+#if defined(__BYTE_ORDER__) && (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)
       unsigned all : 1;
       unsigned unused : 3;
       unsigned set : 1;