When I am fixing GDB's inf-call in one port, I find tests to _Complex
type is quite limited, especially on argument passing, there is none.
This patch is to add more tests to _Complex type on argument passing and
vararg support.

Of course, these changes can be split, and moved to callfuncs.exp and
varargs.exp respectively.  I don't know to what extent _Complex is
supported on all GDB ports, so I put all _Complex related stuff into
complex.exp.

I run this case on these three systems I have, and some problems are
exposed:

i686-pc-linux-gnu: two SIGSEGV
FAIL: gdb.base/complex.exp: print find_max_double_real(4, dc1, dc2, dc3,
dc4)
FAIL: gdb.base/complex.exp: print complex_double_on_stackprint

armv7l-unknown-linux-gnueabi: four SIGSEGV
FAIL: gdb.base/complex.exp: print find_max_float_real(4, fc1, fc2, f3, f4)
FAIL: gdb.base/complex.exp: print find_max_double_real(4, dc1, dc2, dc3,
dc4)
FAIL: gdb.base/complex.exp: print complex_float_on_stackprint
FAIL: gdb.base/complex.exp: print complex_double_on_stackprint

x86_64-unknown-linux-gnu:
FAIL: gdb.base/complex.exp: print find_max_float_real(4, fc1, fc2, f3, f4)
FAIL: gdb.base/complex.exp: print find_max_double_real(4, dc1, dc2, dc3,
dc4)
FAIL: gdb.base/complex.exp: print complex_float_on_stackprint
FAIL: gdb.base/complex.exp: print complex_double_on_stackprint

This case causes new fails, so shall I kfail it?  Comments are welcome.

-- 
Yao (齐尧)