default sysroot per target?

Is there a way to configure the clang build (either autotools+make or
CMake) such that the resulting clang will have a different default
sysroot for each target triple?

For example, in each pair of lines below, if the user enters first
line, it has the meaning of the second:

clang --sysroot=/

clang -target arm-linux-androideabi
clang -target arm-linux-androideabi --sysroot=$NDK/platforms/android-14/arch-arm

clang -target arm-none-linux-gnueabi
clang -target arm-none-linux-gnueabi --sysroot=$ARMLINUX/arm-none-linux-gnueabi


Not right now, but it seems like something reasonable to add a syntax for.