fix check if gcc is actually clang

New macro FP_CHECK_GCC_IS_CLANG checks to see if the compiler given
with the argument --with-gcc is actually clang.
simplify FP_CPP_FLAGS_WITH_VAL_DEFAULTED

The only value for the second parameter is "cpp-flags" so
we might as well substitute that for $2.
Adding CPP and CPP-Flags to configure step, ghc settings file, and associated dyn flags support
now automatically sets cpp-flags correctly when cpp it set to one of gcc, clang, or cpphs.
for unknow cpp, issues warning if —with-cpp-flags=FLAGS isn’t set explictly
remove redundant spaces at start of flags
apply hvr's patch

fixes clang 3.1 segfault