Never treat the main file as a C header.  Make sure that the main
source file is not added to the list of include files if a preprocessed
source file is being compiled.

See: https://github.com/PHHargrove/upc2c/commit/32f34f66d2987feea4798d1638885cd9da403586
Merge branch 'master' of https://github.com/Intrepid/upc2c