Set CMAKE_SYSTEM_PROCESSOR for riscv64 (#46558)

Author: jacogasp

scripts/toolchains/linux.cmake

@@ -65,6 +65,25 @@ if(NOT _VCPKG_LINUX_TOOLCHAIN)
             endif()
             message(STATUS "Cross compiling arm64 on host ${CMAKE_HOST_SYSTEM_PROCESSOR}, use cross compiler: ${CMAKE_CXX_COMPILER}/${CMAKE_C_COMPILER}")
         endif()
+    elseif(VCPKG_TARGET_ARCHITECTURE STREQUAL "riscv64")
+        set(CMAKE_SYSTEM_PROCESSOR riscv64 CACHE STRING "")
+        if(CMAKE_HOST_SYSTEM_NAME STREQUAL "Linux" AND NOT CMAKE_HOST_SYSTEM_PROCESSOR STREQUAL "riscv64")
+
+            if(NOT DEFINED CMAKE_CXX_COMPILER)
+                set(CMAKE_CXX_COMPILER "riscv64-linux-gnu-g++")
+            endif()
+            if(NOT DEFINED CMAKE_C_COMPILER)
+                set(CMAKE_C_COMPILER "riscv64-linux-gnu-gcc")
+            endif()
+            if(NOT DEFINED CMAKE_ASM_COMPILER)
+                set(CMAKE_ASM_COMPILER "riscv64-linux-gnu-gcc")
+            endif()
+            if(NOT DEFINED CMAKE_ASM-ATT_COMPILER)
+                set(CMAKE_ASM-ATT_COMPILER "riscv64-linux-gnu-as")
+            endif()
+            message(STATUS "Cross compiling riscv64 on host ${CMAKE_HOST_SYSTEM_PROCESSOR}, use cross compiler: ${CMAKE_CXX_COMPILER}/${CMAKE_C_COMPILER}")
+        endif()
+
     endif()
 
     if(CMAKE_HOST_SYSTEM_NAME STREQUAL "Linux" AND CMAKE_SYSTEM_PROCESSOR STREQUAL CMAKE_HOST_SYSTEM_PROCESSOR)