test: fix dynamic modules loading on macOS

Since the auxiliary libraries are built as dynamically loaded modules on
macOS instead of shared libraries as it is done on Linux and BSD,
another environment variable should be used to guide `ffi.load()` while
searching the extension. Hence the paths are set in test need to be set
to `DYLD_LIBRARY_PATH` variable instead of `LD_LIBRARY_PATH` on macOS.

test/app-tap/gh-1700-abort-recording-on-fiber-switch.test.lua

@@ -25,17 +25,19 @@ if #arg == 0 then
 
   test:plan(#checks)
 
+  local libext = package.cpath:match('?.(%a+);')
   local vars = {
     LUABIN = arg[-1],
     SCRIPT = arg[0],
     -- To support out-of-source build use relative paths in repo
     PATH   = arg[-1]:gsub('src/tarantool$', 'test/app-tap'),
-    SUFFIX = package.cpath:match('?.(%a+);'),
+    SUFFIX = libext,
   }
 
   local cmd = string.gsub('LUA_CPATH="$LUA_CPATH;<PATH>/?.<SUFFIX>" ' ..
                           'LUA_PATH="$LUA_PATH;<PATH>/?.lua" ' ..
-                          'LD_LIBRARY_PATH=<PATH> ' ..
+                          ((libext == 'dylib' and 'DYLD' or 'LD') ..
+                           '_LIBRARY_PATH=<PATH> ') ..
                           '<LUABIN> 2>&1 <SCRIPT>', '%<(%w+)>', vars)
 
   for _, ch in pairs(checks) do