testsuite/libffi.closures: Fix PowerPC 64 (#709)
-mlong-double-128 is only supported on glibc.
This test still passes on glibc targets, and now passes on musl targets
as well (which uses 64-bit ldbl).
Use CHECK to assert more things in test suite (#654)
* Use CHECK to assert more things in test suite
* Use snprintf instead of sprintf
* Fix va_struct1 and va_struct3