strange handling of invalid pre-processor directives

[Thomas R. Truscott]

/*
 * This file compiles without complaint,
 * despite the "elsewhere" and "elifndef" preprocessor directives.
 * I think there should be a diagnostic.
 * And/or gcc could support elifdef and elifndef
 * as extensions to the pre-processor language.
 */

#if 0
  #error surprise
#elsewhere
  #error elsewhere??
#endif

#ifdef this
  #error this
#elifndef that
  #error not that
#endif