testsuite: Add ABIs to the test matrix; unify tests across ABIs

This eliminates all the *_win32.c tests in favor of the tests they were
branched from, and expands test coverage to run many more tests on
stdcall, thiscall, and fastcall.

This same mechanism also supports testing any other target that has
multiple ABIs.

testsuite/libffi.call/many.c

@@ -11,19 +11,7 @@
 #include <float.h>
 #include <math.h>
 
-static float many(float f1,
-		  float f2,
-		  float f3,
-		  float f4,
-		  float f5,
-		  float f6,
-		  float f7,
-		  float f8,
-		  float f9,
-		  float f10,
-		  float f11,
-		  float f12,
-		  float f13)
+static float ABI_ATTR many(float f1, float f2, float f3, float f4, float f5, float f6, float f7, float f8, float f9, float f10, float f11, float f12, float f13)
 {
 #if 0
   printf("%f %f %f %f %f %f %f %f %f %f %f %f %f\n",
@@ -52,7 +40,7 @@ int main (void)
     }
 
     /* Initialize the cif */
-    CHECK(ffi_prep_cif(&cif, FFI_DEFAULT_ABI, 13, 
+    CHECK(ffi_prep_cif(&cif, ABI_NUM, 13,
 		       &ffi_type_float, args) == FFI_OK);
 
     ffi_call(&cif, FFI_FN(many), &f, values);