When I try to ./configure some programs (but not all), I keep running into the same conftest errors. An example (FLTK 1.1.5rc1):

........................................................................................
configure:2253: gcc -c conftest.c >&5
conftest.c:2: error: parse error before "me"
configure:2256: $? = 1
configure: failed program was:
| #ifndef __cplusplus
| choke me
| #endif
configure:2417: checking for g++
..........................................................................................

Which always leads to:

..........................................................................................
configure:2653: g++ -c conftest.cc >&5
configure: In function `int main()':
configure:2648: error: `exit' undeclared (first use this function)
configure:2648: error: (Each undeclared identifier is reported only once for each function it appears in.)
configure:2656: $? = 1
configure: failed program was:
| #line 2636 "configure"
| /* confdefs.h. */
............................................................................................

Later, I get several more errors. The exact errors depend on whatever package I am trying to install. Anyone have any ideas?