Reduce strength of clang requirement to 3.0

* All that is required is that clang binary IR is compatible
  with llvm 3.7.
Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>

CMakeLists.txt

@@ -20,8 +20,8 @@ endif()
 execute_process(COMMAND ${CLANG} --version OUTPUT_VARIABLE CLANG_VERSION_RAW)
 string(REGEX MATCH "[0-9]+[.][0-9]+[.][0-9]+" CLANG_VERSION ${CLANG_VERSION_RAW})
 message(STATUS "Found CLANG: ${CLANG} (found version \"${CLANG_VERSION}\")")
-if (CLANG_VERSION VERSION_LESS 3.5.0)
-  message(FATAL_ERROR "requires clang version >= 3.5.0, ${CLANG_VERSION} found")
+if (CLANG_VERSION VERSION_LESS 3.0.0)
+  message(FATAL_ERROR "requires clang version >= 3.0.0, ${CLANG_VERSION} found")
 endif()
 
 set(CMAKE_C_FLAGS "-Wall")