tools: Export LLVM flags for kernel build

[no1wudi]

##Summary

• Added LLVM_ARCHTYPE, LLVM_CPUTYPE, and LLVM_ABITYPE to the exported build configuration in both Export.mk and mkexport.sh
• These flags are now included in the generated makeinfo.sh, Make.defs, and target.cmake files during the export process

##Impact

• Enables LLVM-specific build configurations to be properly exported and used in kernel builds
• Improves compatibility with LLVM-based toolchains by ensuring necessary architecture, CPU, and ABI information is available during the build process
• No functional changes for non-LLVM builds, as these flags are only used when LLVM toolchains are specified

Testing

GitHub CI and local board

[no1wudi]

@lupyuen Could you try this patch for rust support with kernel mode?

[lupyuen]

Sorry @no1wudi the hello_rust_cargo ELF seems to be missing from apps/bin? Other apps are OK. Thanks :-)
https://gist.github.com/lupyuen/98e110d5228c9d2eaee16e8a3734055b

$ tools/configure.sh rv-virt:knsh64

nsh> uname -a
NuttX 10.0.1 caebb3ecc2 Jan 26 2025 12:41:22 risc-v rv-virt

nsh> hello
Hello, World!!

nsh> hello_rust_cargo
nsh: hello_rust_cargo: command not found

$ ls -l ../apps/bin
total 496
-rwxr-xr-x@ 1 luppy  staff  21504 Jan 26 12:41 getprime
-rwxr-xr-x@ 1 luppy  staff   9048 Jan 26 12:41 hello
-rwxr-xr-x@ 1 luppy  staff  64864 Jan 26 12:41 init
-rwxr-xr-x@ 1 luppy  staff  83296 Jan 26 12:41 ostest
-rwxr-xr-x@ 1 luppy  staff  64864 Jan 26 12:41 sh

$ grep HELLO_RUST_CARGO .config
CONFIG_EXAMPLES_HELLO_RUST_CARGO=y
CONFIG_EXAMPLES_HELLO_RUST_CARGO_PROGNAME="hello_rust_cargo"
CONFIG_EXAMPLES_HELLO_RUST_CARGO_PRIORITY=100
CONFIG_EXAMPLES_HELLO_RUST_CARGO_STACKSIZE=16384

[no1wudi]

So for this issue it's not enough by just add LLVM relative flags, it can make Rust app build as static lib, but need further work to build an ELF file from Rust toolchain directly.