[CMake][Fuchsia] Revert back to using normalized triples (#98189)

We switched to denormalized triples in #89425 but that introduced a lot
of downstream issues so switch back to normalized triples.

Author: petrhosek

clang/cmake/caches/Fuchsia-stage2.cmake

@@ -141,7 +141,7 @@ if(WIN32 OR LLVM_WINSYSROOT)
   set(RUNTIMES_${target}_CMAKE_MODULE_LINKER_FLAGS ${WINDOWS_LINK_FLAGS} CACHE STRING "")
 endif()
 
-foreach(target aarch64-linux-gnu;armv7-linux-gnueabihf;i386-linux-gnu;riscv64-linux-gnu;x86_64-linux-gnu)
+foreach(target aarch64-unknown-linux-gnu;armv7-unknown-linux-gnueabihf;i386-unknown-linux-gnu;riscv64-unknown-linux-gnu;x86_64-unknown-linux-gnu)
   if(LINUX_${target}_SYSROOT)
     # Set the per-target builtins options.
     list(APPEND BUILTIN_TARGETS "${target}")