Merge pull request #22547 from dkurt:riscv_toolchain

Detect RISC-V compiler from PATH environment variable

platforms/linux/riscv64-gcc.toolchain.cmake

 set(CMAKE_SYSTEM_NAME Linux)
 set(CMAKE_SYSTEM_PROCESSOR riscv64)
 
-set(RISCV_GCC_INSTALL_ROOT /opt/RISCV CACHE PATH "Path to GCC for RISC-V cross compiler installation directory")
-set(CMAKE_SYSROOT ${RISCV_GCC_INSTALL_ROOT}/sysroot CACHE PATH "RISC-V sysroot")
+if(NOT DEFINED CMAKE_C_COMPILER)
+  find_program(CMAKE_C_COMPILER NAMES riscv64-unknown-linux-gnu-gcc
+                                PATHS /opt/RISCV/bin ENV PATH)
+endif()
+
+if(NOT DEFINED CMAKE_CXX_COMPILER)
+  find_program(CMAKE_CXX_COMPILER NAMES riscv64-unknown-linux-gnu-g++
+                                  PATHS /opt/RISCV/bin ENV PATH)
+endif()
 
-set(CMAKE_C_COMPILER ${RISCV_GCC_INSTALL_ROOT}/bin/riscv64-unknown-linux-gnu-gcc)
-set(CMAKE_CXX_COMPILER ${RISCV_GCC_INSTALL_ROOT}/bin/riscv64-unknown-linux-gnu-g++)
+get_filename_component(RISCV_GCC_INSTALL_ROOT ${CMAKE_C_COMPILER} DIRECTORY)
+get_filename_component(RISCV_GCC_INSTALL_ROOT ${RISCV_GCC_INSTALL_ROOT} DIRECTORY)
+
+set(CMAKE_SYSROOT ${RISCV_GCC_INSTALL_ROOT}/sysroot CACHE PATH "RISC-V sysroot")
 
 # Don't run the linker on compiler check
 set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY)