alpha: Add support for complex types

testsuite/libffi.call/call.exp

@@ -27,6 +27,7 @@ run-many-tests $tlist ""
 # ??? We really should preprocess ffi.h and grep
 # for FFI_TARGET_HAS_COMPLEX_TYPE.
 if { [istarget aarch64*]
+     || [istarget alpha*]
      || [istarget i?86*]
      || [istarget s390*]
      || [istarget x86_64*] } {

testsuite/libffi.call/cls_complex_va_float.c

@@ -6,5 +6,11 @@
 
 /* { dg-do run } */
 
+/* Alpha splits _Complex into two arguments.  It's illegal to pass
+   float through varargs, so _Complex float goes badly.  In sort of
+   gets passed as _Complex double, but the compiler doesn't agree
+   with itself on this issue.  */
+/* { dg-do run { xfail alpha*-*-* } } */
+
 #include "complex_defs_float.inc"
 #include "cls_complex_va.inc"