chore: import upstream snapshot with attribution

platforms/linux/riscv-gnu.toolchain.cmake

@@ -0,0 +1,54 @@
+if(COMMAND toolchain_save_config)
+  return() # prevent recursive call
+endif()
+
+set(CMAKE_SYSTEM_NAME Linux)
+set(CMAKE_SYSTEM_VERSION 1)
+if(NOT DEFINED CMAKE_SYSTEM_PROCESSOR)
+  set(CMAKE_SYSTEM_PROCESSOR riscv64)
+else()
+  #message("CMAKE_SYSTEM_PROCESSOR=${CMAKE_SYSTEM_PROCESSOR}")
+endif()
+
+include("${CMAKE_CURRENT_LIST_DIR}/gnu.toolchain.cmake")
+
+if(NOT "x${GCC_COMPILER_VERSION}" STREQUAL "x")
+  set(__GCC_VER_SUFFIX "-${GCC_COMPILER_VERSION}")
+endif()
+
+if(NOT DEFINED GNU_MACHINE)
+  set(GNU_MACHINE riscv64-unknown-linux-gnu CACHE STRING "GNU compiler triple")
+endif()
+
+if(NOT DEFINED TOOLCHAIN_COMPILER_LOCATION_HINT)
+  set(TOOLCHAIN_COMPILER_LOCATION_HINT PATHS /opt/riscv/bin ENV PATH)
+endif()
+
+find_program(CMAKE_C_COMPILER NAMES ${GNU_MACHINE}-gcc${__GCC_VER_SUFFIX} PATHS ${TOOLCHAIN_COMPILER_LOCATION_HINT})
+find_program(CMAKE_CXX_COMPILER NAMES ${GNU_MACHINE}-g++${__GCC_VER_SUFFIX} PATHS ${TOOLCHAIN_COMPILER_LOCATION_HINT})
+find_program(CMAKE_LINKER NAMES ${GNU_MACHINE}-ld${__GCC_VER_SUFFIX} ${GNU_MACHINE}-ld PATHS ${TOOLCHAIN_COMPILER_LOCATION_HINT})
+find_program(CMAKE_AR NAMES ${GNU_MACHINE}-ar${__GCC_VER_SUFFIX} ${GNU_MACHINE}-ar PATHS ${TOOLCHAIN_COMPILER_LOCATION_HINT})
+
+if(NOT CMAKE_C_COMPILER OR NOT CMAKE_CXX_COMPILER OR NOT CMAKE_LINKER OR NOT CMAKE_AR)
+  message(FATAL_ERROR "\
+    One of RISC-V toolchain components have not been found:
+      CMAKE_C_COMPILER=${CMAKE_C_COMPILER}
+      CMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER}
+      CMAKE_LINKER=${CMAKE_LINKER}
+      CMAKE_AR=${CMAKE_AR}
+    Use PATH environment variable and/or GNU_MACHINE, TOOLCHAIN_COMPILER_LOCATION_HINT and others cmake variables to help CMake find them.")
+endif()
+
+if(NOT DEFINED RISCV_SYSROOT)
+  get_filename_component(_base_dir ${CMAKE_C_COMPILER} DIRECTORY)
+  get_filename_component(_base_dir ${_base_dir} DIRECTORY)
+  set(RISCV_SYSROOT ${_base_dir}/sysroot CACHE PATH "RISC-V sysroot")
+endif()
+
+set(CMAKE_SYSROOT "${RISCV_SYSROOT}")
+set(CMAKE_FIND_ROOT_PATH ${CMAKE_FIND_ROOT_PATH} ${RISCV_SYSROOT})
+
+set(TOOLCHAIN_CONFIG_VARS ${TOOLCHAIN_CONFIG_VARS}
+    RISCV_SYSROOT
+)
+toolchain_save_config()