X11: Fix sonames for loaded libraries on OpenBSD

The OpenBSD ports tree assigns its own soname version numbers, so the
hardcoded sonames GLFW uses to load libraries on non-macOS Unices are
often incorrect.  Instead OpenBSD recommends that run-time loading
should leave out the version numbers entirely.  The OpenBSD ld.so then
finds the correct library.

This upstreams the ports tree fixes for Xcursor and EGL, and adds the
corresponding fix for all other run-time loaded library sonames.

Tested on OpenBSD 7.0.

This issue was initially reported on IRC.

(cherry picked from commit 7d060ba4f1)

src/glx_context.c

@@ -260,6 +260,8 @@ GLFWbool _glfwInitGLX(void)
         _GLFW_GLX_LIBRARY,
 #elif defined(__CYGWIN__)
         "libGL-1.so",
+#elif defined(__OpenBSD__)
+        "libGL.so",
 #else
         "libGL.so.1",
         "libGL.so",