Rearrange and fixup abstraction layer

- Replace os_result by dds_retcode_t and move DDS return code defines down.
  Eliminates the need to convert between different return code types.

- Move dds_time_t down and remove os_time.
  Eliminates the need to convert between different time representations and
  reduces code duplication.

- Remove use of Microsoft source-code annotation language (SAL).
  SAL annotations are Microsoft specific and not very well documented. This
  makes it very difficult for contributers to write.

- Rearrange the abstraction layer to be feature-based. The previous layout
  falsely assumed that the operating system dictates which implementation is
  best suited. For general purpose operating systems this is mostly true, but
  embedded targets require a slightly different approach and may not even offer
  all features. The new layout makes it possible to mix-and-match feature
  implementations and allows for features to not be implemented at all.

- Replace the os prefix by ddsrt to avoid name collisions.

- Remove various portions of unused and unwanted code.

- Export thread names on all supported platforms.

- Return native thread identifier on POSIX compatible platforms.

- Add timed wait for condition variables that takes an absolute time.

- Remove system abstraction for errno. The os_getErrno and os_setErrno were
  incorrect. Functions that might fail now simply return a DDS return code
  instead.

- Remove thread-specific memory abstraction. os_threadMemGet and accompanying
  functions were a mess and their use has been eliminated by other changes in
  this commit.

- Replace attribute (re)defines by ddsrt_ prefixed equivalents to avoid name
  collisions and problems with faulty __nonnull__ attributes.

Signed-off-by: Jeroen Koekkoek <jeroen@koekkoek.nl>

src/core/ddsc/tests/entity_api.c

@@ -9,7 +9,7 @@
  *
  * SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
  */
-#include "ddsc/dds.h"
+#include "dds/dds.h"
 #include "CUnit/Test.h"
 
 /* We are deliberately testing some bad arguments that SAL will complain about.
@@ -338,7 +338,7 @@ CU_Test(ddsc_entity, get_entities, .init = create_entity, .fini = delete_entity)
 CU_Test(ddsc_entity, get_domainid, .init = create_entity, .fini = delete_entity)
 {
     dds_return_t status;
-    dds_domainid_t id;
+    dds_domainid_t id = -1;
 
     /* Check getting ID with bad parameters. */
     status = dds_get_domainid (0, NULL);
@@ -351,7 +351,7 @@ CU_Test(ddsc_entity, get_domainid, .init = create_entity, .fini = delete_entity)
     /* Get and check the domain id. */
     status = dds_get_domainid (entity, &id);
     cu_assert_status_eq(status, DDS_RETCODE_OK);
-    CU_ASSERT_EQUAL_FATAL(id, 0);
+    CU_ASSERT_FATAL(id != -1);
 }
 
 CU_Test(ddsc_entity, delete, .init = create_entity)