Don't use xcrun for setting IOSSDK

Makefile.libretro

@@ -41,7 +41,7 @@ else ifeq ($(platform), ios)
    DEFINES := -DIOS
 
 ifeq ($(IOSSDK),)
-   IOSSDK := $(shell xcrun -sdk iphoneos -show-sdk-path)
+   IOSSDK := $(shell xcodebuild -version -sdk iphoneos Path)
 endif
 	CC = clang -arch armv7 -isysroot $(IOSSDK)
 else ifeq ($(platform), theos_ios)