add clang and build with it

Signed-off-by: june-fish <git@june.fish>

Author: june-fish

flake.nix

@@ -45,6 +45,8 @@
               pkgs.perl
               pkgs.pkgsCross.riscv64-embedded.stdenv.cc.bintools.bintools
               pkgs.pkgsCross.riscv64-embedded.stdenv.cc.cc
+              pkgs.pkgsCross.riscv64-embedded.llvmPackages.stdenv.cc.bintools.bintools
+              pkgs.pkgsCross.riscv64-embedded.llvmPackages.stdenv.cc.cc
               pkgs.python3
             ];
 
@@ -101,7 +103,8 @@
             pkgs.tio
           ];
           shellHook = ''
-            export CC=riscv64-none-elf-gcc
+            export CC=clang
+            export CFLAGS="-target riscv64-none-elf -std=c23"
             export OBJDUMP=riscv64-none-elf-objdump
             export STRIP=riscv64-none-elf-strip
           '';