OSX vs OpenMP : implement workaround to fix crashes when using mop from a background thread

Fix# 20043 & 20392

The issue is that OSX lib does not implement TLS (Thread Local Storage), so  libgomp uses pthread functions to read/write thread specific vars.
But this implementation is currently (gcc 4.2) buggy : the write function is called only at lib start (in main thread), and the var is undefined for background thread.

The workaround is to perform this gomp_tls_key var write at beginning of background threads that use openMP. (Currently: render & fluidsim)

intern/elbeem/CMakeLists.txt

@@ -33,9 +33,9 @@ IF(WINDOWS)
 		ADD_DEFINITIONS(-DUSE_MSVC6FIXES)
 ENDIF(WINDOWS)
 
-IF(WITH_OPENMP AND NOT APPLE)
+IF(WITH_OPENMP)
 		ADD_DEFINITIONS(-DPARALLEL=1)
-ENDIF(WITH_OPENMP AND NOT APPLE)
+ENDIF(WITH_OPENMP)
 
 BLENDERLIB_NOLIST(bf_elbeem "${SRC}" "${INC}")
 #, libtype='blender', priority=0 )

intern/elbeem/SConscript

@@ -8,8 +8,7 @@ sources = env.Glob('intern/*.cpp')
 defs = 'NOGUI ELBEEM_BLENDER=1'
 
 if env['WITH_BF_OPENMP']:
-    if env['OURPLATFORM'] != 'darwin':
-        defs += ' PARALLEL'
+    defs += ' PARALLEL'
 
 if env['OURPLATFORM'] in ('win32-vc', 'win64-vc'):
     defs += ' USE_MSVC6FIXES'