I am using Xcode to build an old code and specify SDKROOT=/Developer/SDKs/MacOSX"${HOST_VERSION}".sdk/
I want to specify SDKROOT for latest SDK that comes pre-installed (?) on the system. e.g. I am on 10.8 already and I want to specify SDKROOT with -syslibroot, but there is no such SDK in /Developer/SDKs/. Should i just ignore syslibroot altogether if SDK_VERSION == HOST_VERSION?
Newer Xcode versions have the SDKs inside the Xcode.app bundle, e.g.
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.8.sdk
You get the list of installed SDKs together with their path by running
xcodebuild -sdk -version
from the command line.
If you have installed the "Command Line Tools" (Xcode Preferences -> Downloads -> Components) then compiling without "-syslibroot" should be equivalent to compiling against the latest SDK.
See the help to the "Command Line Tools" package:
Downloading this package will install copies of the core command line tools and system headers into system folders, including the LLVM compiler, linker, and build tools.