cygwin: check for wrong gcc-4, --disable-shared

replace wrong gcc-4/g++-4 with gcc/g++. GH #1116
set proper libparrot_ldflags for --disable-shared
  (the static lib is in blib/lib)
fix wrong $disable_shared logic in defaults
Merge branch 'smoke-me/cygwin-gcc4-gh1116' into rurban/gcdebug-gh1108