This commit addresses these kind of errors:
portability: Passing NULL after the last typed argument to a variadic function leads to undefined behaviour. [varFuncNullUB]
Reason is that C does not guarantee that all pointer types are the same
size. See C99 6.2.5(27). cppcheck requires some sort of cast when NULL
is used as the last argument in a variadic list.
These Coverity warnings all relate to the user of g_setenv() where the
return result isn't checked.
An additional void function g_setenv_log() is provided which logs
failures to set environment variables, and returns no status. This is
used in all the places where g_setenv_is currently called.
matt335672