I don't have access to source so my comment will be based only on diffs from above mentioned revisions.
r80969:
- AC_LANG_PROGRAM ... with main function in body . It is legal as I don't know C compiler that fail to compile code like ...int main() { int main() {...} ...} but is better to left body empty. Counted three times. All those cases tests for compiler flags and I think that AC_LANG_SOURCE is enough.

- body include  #include "confdefs.h" - may be buggy (before) and now AC_LANG_PROGRAM will add all defines. Counted any times. I think that is save to remove  #include "confdefs.h" from all those test cases.