The new test driver in <support/test-driver.c> has feature parity with
the old one. The main difference is that its hooking mechanism is
based on functions and function pointers instead of macros. This
commit also implements a new environment variable, TEST_COREDUMPS,
which disables the code which disables coredumps (that is, it enables
them if the invocation environment has not disabled them).
<test-skeleton.c> defines wrapper functions so that it is possible to
use existing macros with the new-style hook functionality.
This commit changes only a few test cases to the new test driver, to
make sure that it works as expected.
The test case dlfcn/bug-atexit3-lib.cc calls write and doesn't check the
result. When building with GCC 6.2, this generates a warning in 'make
check', which is treated as an error. This patch replaces the call to
write with a call to write_message.
Tested for powerpc64le.
