Meta: Do not set -march=native on riscv64

Author: https://github.com/evelance
Commit: b50b89b4a8
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/6302
Reviewed-by: https://github.com/ADKaster
Reviewed-by: https://github.com/gmta ✅
Reviewed-by: https://github.com/spholz

Meta/CMake/common_compile_options.cmake

@@ -61,6 +61,11 @@ elseif (ENABLE_CI_BASELINE_CPU)
     elseif (CMAKE_SYSTEM_PROCESSOR STREQUAL "x86_64")
         add_cxx_compile_options(-march=x86-64-v3)
     endif()
+elseif (CMAKE_SYSTEM_PROCESSOR STREQUAL "riscv64")
+    # On RISC-V the generic -march=native is not yet supported and both gcc and clang require an explicit
+    # ISA or target string. Unfortunately hardware probing is also neither easy nor reliable at the moment.
+    # For the time being use the defaults for the best compatibility with existing hardware and toolchains.
+    # FIXME: Remove this branch once -march=native is supported.
 else()
     # In all other cases, compile for the native architecture of the host system.
     add_cxx_compile_options(-march=native)