fix PR4049, a crash on invalid, by making sema install the right number of

parameters in a functiondecl, even if the decl is invalid and has a confusing
Declarator.  On the testcase, we now emit one beautiful diagnostic:

t.c:2:1: error: unknown type name 'unknown_type'
unknown_type f(void*)
^

GCC 4.0 produces:

t.c:2: error: syntax error before ‘f’
t.c: In function ‘f’:
t.c:2: error: parameter name omitted

and GCC 4.2:

t.c:2: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘f’

llvm-svn: 70016