Bug 1883615 - Move libdl checks to moz.configure and make libdl dependencies explicit r=glandium

The -ldl flag was previously set globally, it's now set for the libs
that use it.

Also rationalize the difference between HAVE_DLOPEN and HAVE_DLFCN_H.

Differential Revision: https://phabricator.services.mozilla.com/D203594

memory/replace/logalloc/replay/moz.build

@@ -82,6 +82,8 @@ DEFINES["IMPL_MFBT"] = True
 if CONFIG["MOZ_NEEDS_LIBATOMIC"]:
     OS_LIBS += ["atomic"]
 
+OS_LIBS += CONFIG["DL_LIBS"]
+
 DisableStlWrapping()
 
 include("/mozglue/build/replace_malloc.mozbuild")