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/strlen2.c

@@ -0,0 +1,49 @@
+/* Area:	ffi_call
+   Purpose:	Check strlen function call with additional arguments.
+   Limitations:	none.
+   PR:		none.
+   Originator:	From the original ffitest.c  */
+
+/* { dg-do run } */
+
+#include "ffitest.h"
+
+static size_t ABI_ATTR my_f(char *s, float a)
+{
+  return (size_t) ((int) strlen(s) + (int) a);
+}
+
+int main (void)
+{
+  ffi_cif cif;
+  ffi_type *args[MAX_ARGS];
+  void *values[MAX_ARGS];
+  ffi_arg rint;
+  char *s;
+  float v2;
+  args[0] = &ffi_type_pointer;
+  args[1] = &ffi_type_float;
+  values[0] = (void*) &s;
+  values[1] = (void*) &v2;
+  
+  /* Initialize the cif */
+  CHECK(ffi_prep_cif(&cif, ABI_NUM, 2,
+		       &ffi_type_sint, args) == FFI_OK);
+  
+  s = "a";
+  v2 = 0.0;
+  ffi_call(&cif, FFI_FN(my_f), &rint, values);
+  CHECK(rint == 1);
+  
+  s = "1234567";
+  v2 = -1.0;
+  ffi_call(&cif, FFI_FN(my_f), &rint, values);
+  CHECK(rint == 6);
+  
+  s = "1234567890123456789012345";
+  v2 = 1.0;
+  ffi_call(&cif, FFI_FN(my_f), &rint, values);
+  CHECK(rint == 26);
+  
+  exit(0);
+}