Use RTLD_DEFAULT to unbreak on non-Linux

[jbeich]

clinfo fails to look up available libOpenCL symbols and falls back to 1.0.

clinfo/src/clinfo.c

Lines 3040 to 3042 in 59d0daf

	/* Initialize icdl_data ret versions */
	icdl.detected_version = 10;
	icdl.reported_version = 0;

$ pkg install clinfo intel-compute-runtime
$ clinfo
[...]
        NOTE:   your OpenCL library declares to support OpenCL 2.2,
                but it seems to support up to OpenCL 1.0 only.
        NOTE:   your OpenCL library only supports OpenCL 1.0,
                but some installed platforms support OpenCL 3.0.
                Programs using 3.0 features may crash
                or behave unexpectedly

$ pkg info -x opencl ocl
opencl-2.2_2
ocl-icd-2.2.12

https://github.com/DragonFlyBSD/DragonFlyBSD/blob/v5.8.3/include/dlfcn.h#L59-L65
https://github.com/freebsd/freebsd/blob/releng/12.2/include/dlfcn.h#L62-L67
https://github.com/NetBSD/src/blob/2518280dc5e5/include/dlfcn.h#L84-L89
https://github.com/openbsd/src/blob/88eb9092f38b/include/dlfcn.h#L46-L51
https://github.com/illumos/illumos-gate/blob/4e0c5eff9af3/usr/src/head/dlfcn.h#L127-L137

[Oblomov]

Ugh, thanks for catching this, I cherry picked your comment and pushed to the latest master.

(I keep telling myself that I should get me a BSD VM for testing these stuff locally when making big changes, but I keep procrastinating.)