Scons: run `clang -Wall -fsyntax-only` in clang-analyze

The `clang -fsyntax-only` will give us additional warning messages in
the console.
Scons: add a custom tool to do clang static analyze

Bsps can use the clang analyzer as a tool:

    env = Environment(toolpath=[os.path.join(RTT_ROOT, 'tools',
                      'tools')], tools = ['clang-analyze'])

When building the project, the static analyzer will be called to check
all the C code. The warnings are print to stderr.
simulator: add clang-analyze tool support

When CROSS_TOOL or 'RTT_CC' env is setted to 'clang-analyze', it will
use Clang to check the codes.