CoreFx hardcodes paths in the Native scripts.

[ViktorHofer]

• src/libraries/Native/Unix/gen-buildsys-clang.sh:19
• src/libraries/Native/Windows/clrcompression/CMakeLists.txt:87
• src/libraries/Native/build-native.cmd:7
• src/libraries/Native/build-native.sh:177

cc @safern

[ViktorHofer]

@eiriktsarpalis might take a look.