glp_version: do not initialize env

Hello Andrew,

if a multithreaded application wants to determine if GLPK supports a
feature we now supply glp_config which does not initialize env.
I guess we should do the same for glp_version.

This makes env smaller and can safely be called even if the library is
not TLS enabled.

#define str(s) # s
#define xstr(s) str(s)

const char *glp_version(void)
{     return xstr(GLP_MAJOR_VERSION) "." xstr(GLP_MINOR_VERSION);
}

Best regards

Heinrich