Add magic -D switch to work around OS X 10.5 bug in ucontext.h

indra/cmake/00-Common.cmake

@@ -179,11 +179,17 @@ endif (LINUX)
 
 
 if (DARWIN)
-  add_definitions(-DLL_DARWIN=1)
+  # NOTE (per http://lists.apple.com/archives/darwin-dev/2008/Jan/msg00232.html):
+  # > Why the bus error? What am I doing wrong? 
+  # This is a known issue where getcontext(3) is writing past the end of the
+  # ucontext_t struct when _XOPEN_SOURCE is not defined (rdar://problem/5578699 ).
+  # As a workaround, define _XOPEN_SOURCE before including ucontext.h.
+  add_definitions(-DLL_DARWIN=1 -D_XOPEN_SOURCE)
   set(CMAKE_CXX_LINK_FLAGS "-Wl,-headerpad_max_install_names,-search_paths_first")
   set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_CXX_LINK_FLAGS}")
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -mlong-branch")
-  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -mlong-branch")
+  set(DARWIN_extra_cstar_flags "-mlong-branch")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${DARWIN_extra_cstar_flags}")
+  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS}  ${DARWIN_extra_cstar_flags}")
   # NOTE: it's critical that the optimization flag is put in front.
   # NOTE: it's critical to have both CXX_FLAGS and C_FLAGS covered.
   set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "-O0 ${CMAKE_CXX_FLAGS_RELWITHDEBINFO}")