When using fc1-test1 for x86_64, I receive an ' error: incompatible types in assignment' from gcc when I try to assign the value of one va_list variable to another. This does not happen on an x86 box running fc1. Attached is a small test case that does nothing useful, but it will error if you try to compile it on x86_64, but not on x86.
Created attachment 97444 [details] Simple test case that fails to compile on x86_64
That testcase is buggy, you cannot do that. If you need to copy va_list objects, you need to use va_copy. See man va_copy for example, or ISO C.