These tests in this patch is about passing _Complex type args and return
_Complex type.

Rerun callfuncs.exp on i686-pc-linux-gnu, and get two new KFAIL and one
FAIL.  This extra FAIL is caused by these two KFAILs.  PR 12783 is opened.

KFAIL: gdb.base/callfuncs.exp: call inferior func with struct - returns
double _Complex (PRMS: gdb/12783)
KFAIL: gdb.base/callfuncs.exp: call inferior func with struct - returns
long double _Complex (PRMS: gdb/12783)

FAIL: gdb.base/callfuncs.exp: gdb function calls preserve register contents

                === gdb Summary ===

# of expected passes            153
# of unexpected failures        1
# of known failures             2

Note that there is no tests about _Complex in aggregate types in this
patch set, because gdb.base/structs.exp can not be extended to cover
_Complex types easily.  I find there is an interesting test on
struct/union in gcc (gcc.dg/compat/struct-layout-1.exp), and still need
some time to see if we can make use of it in gdb tests.

-- 
Yao (齐尧)