Makefile: Fix compiling on macOS

Author: GhostlyDark

projects/unix/Makefile

@@ -122,9 +122,7 @@ ifeq ($(OS), LINUX)
   LDLIBS += -ldl
 endif
 ifeq ($(OS), OSX)
-  #xcode-select has been around since XCode 3.0, i.e. OS X 10.5
-  OSX_SDK_ROOT = $(shell xcode-select -print-path)/Platforms/MacOSX.platform/Developer/SDKs
-  OSX_SDK_PATH = $(OSX_SDK_ROOT)/$(shell ls $(OSX_SDK_ROOT) | tail -1)
+  OSX_SDK_PATH = $(shell xcrun --sdk macosx --show-sdk-path)
 
   ifeq ($(CPU), X86)
     ifeq ($(ARCH_DETECTED), 64BITS)