CXXFeatures: blacklist Borland and Watcom for C++11 compiler flag detection

These compilers do not have a C++11 flag, but check_cxx_compiler_flag()
can't detect because they either will not always complain (Borland) or will
hang (Watcom).
Merge topic 'cxx11' into next

d0bfc5b CXXFeatures: blacklist Borland and Watcom for C++11 compiler flag detection