#160 Add option to set some system defaults during ./configure

[Simon Sobisch]

As discussed earlier and in [https://sourceforge.net/p/open-cobol/discussion/help/thread/2072290f/#c58b/b832/e2a5] it would be nice to set some system defaults during the configure step.

Everything that has to do with compiling (like the maximum number of call parameters) goes to config.h already but we may should add system defaults that are used for general compilations, too - either built-in (for example into defaults.h) and/or via an own configuration (something like config/cobc.defaults) file.

Possible values here:

• defaults for flags (see flags.def)
• defaults for command line options (the -std / -conf used if not passed on command line; warning options or (possible with the -fconf_options), maybe someone want to have the most forgiving compiler by adding -frelax-syntax-checks -flarger-redefines -frelax-level-hierarchy -ftop-level-occurs-clause=ok to this file...)