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/CMakeLists.txt

@@ -51,17 +51,13 @@ include(ddsi/CMakeLists.txt)
 include(ddsc/CMakeLists.txt)
 
 target_link_libraries(ddsc PRIVATE util)
-target_link_libraries(ddsc PRIVATE OSAPI)
+target_link_libraries(ddsc PRIVATE ddsrt)
+target_include_directories(
+  ddsc PUBLIC $<BUILD_INTERFACE:$<TARGET_PROPERTY:ddsrt,INTERFACE_INCLUDE_DIRECTORIES>>)
 
 # SOVERSION should increase on incompatible ABI change
 set_target_properties(ddsc PROPERTIES VERSION ${PROJECT_VERSION} SOVERSION ${PROJECT_VERSION_MAJOR})
 
-get_target_property(os_api_src_dir OSAPI SOURCE_DIR)
-# We need to expose some of the OS headers as well.
-target_include_directories(ddsc
-    PUBLIC
-        "$<BUILD_INTERFACE:${os_api_src_dir}/include>")
-
 set_target_file_ids(ddsc)
 
 # Create a pseudo-target that other targets (i.e. examples, tests) can depend