Added test for the dtrace program and enables its use if found

Signed-off-by: Daniel A. Steffen <dsteffen@apple.com>

Author: tachoknight

CMakeLists.txt

@@ -67,7 +67,12 @@ endif()
 if(CMAKE_SYSTEM_NAME STREQUAL Android)
   set(ENABLE_DTRACE_DEFAULT OFF)
 else()
-  set(ENABLE_DTRACE_DEFAULT ON)
+  find_program(DTRACEPROG dtrace)
+  if(DTRACEPROG)
+    set(ENABLE_DTRACE_DEFAULT ON)
+  else()
+    set(ENABLE_DTRACE_DEFAULT OFF)
+  endif()
 endif()
 option(ENABLE_DTRACE "enable dtrace support" ${ENABLE_DTRACE_DEFAULT})