toolchain: clang: add -Wno-typedef-redefinition option

Without the -Wno-typedef-redefinition option, clang complains if a
typedef gets redefined in gnu99  mode (since this is officially a C11
feature).

While new versions of GCC do not seem to issue this warning in gnu99
mode anymore. So some existing code with typedef redefined which works
well with GCC will issue this warning.

Similar to what was done in 2354f055.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>