declare getpass in analyzer/sensitive-1.c test

declare getpass in analyzer/sensitive-1.c test

The getpass function is not available on all systems; and not
necessarily declared in unistd.h, as expected by the sensitive-1
analyzer test.

Since this is a compile-only test, it doesn't really matter if the
function is defined in the system libraries.  All we need is a
declaration, to avoid warnings from calling an undeclared function.
This patch adds the declaration, in a way that is most unlikely to
conflict with any existing declaration.

for  gcc/testsuite/ChangeLog

	* gcc.dg/analyzer/sensitive-1.c: Declare getpass.