Clean up/unify the Darwin-based targets

[kirb]

We have 4 different versions of iphone.mk, and holy crap, 7 different Darwin-based targets supported on macOS. There’s a high amount of code duplication and inconsistency, such as in #209.

Almost all of each target makefile is exactly the same, especially on macOS, just with the particular target name changed. And for pretty much every instance of xcrun -sdk iphoneos we can just use xcrun, because none of these binaries are SDK-specific any more. SDK scanning might need a cleanup. Non-Xcode cross-compile toolchain logic definitely needs a cleanup.

[sbingner]

I fixed the SDK sort order issue for latest by using:
_IOS_SDKS := $(shell echo $(patsubst $(_XCODE_SDK_DIR)/iPhoneOS%.sdk,%'\n',$(wildcard $(_XCODE_SDK_DIR)/iPhoneOS*.sdk))'\n'$(patsubst $(THEOS_SDKS_PATH)/iPhoneOS%.sdk,%'\n',$(wildcard $(THEOS_SDKS_PATH)/iPhoneOS*.sdk)) | sort -n | paste -s -d" " - )

in makefiles/targets/Darwin/iphone.mk

[kirb]

Done in Theos 2.4.