errors

• configure: error: tag name "CXX" already exists
  Could happen when running ./configure under shell different from bash. Switch to bash shell.
• gcc error: Link tests are not allowed after GCC_NO_EXECUTABLES
  Could happen when running ./configure and having an old version of GNU ld. Switch to a newer version.
• C++ preprocessor "/lib/cpp" fails sanity check error could be caused by absence of CXX environment variable; set CXX=g++ - even if g++ is not used at all or even not present. In some extremly stupid cases g++ should be present, even if it is not used at all (observed on FreeBSD and Darwin).