[RISCV] get toolchain path from enviroment variable

Author: zakk0610

cmake/caches/target-riscv64-linux.cmake

@@ -1,9 +1,7 @@
 set(CMAKE_SYSTEM_NAME Linux)
 set(triple riscv64-unknown-linux-gnu)
-set(tools /work/kaiw/riscv-llvm-rvv-linux)
-set(sysroot ${tools}/sysroot)
+set(tools $ENV{RISCV_TOOL})
 set(cflags "-mcpu=sifive-u77")
-set(CMAKE_SYSROOT ${sysroot})
 set(CMAKE_C_COMPILER  ${tools}/bin/clang CACHE STRING "" FORCE)
 set(CMAKE_CXX_COMPILER ${tools}/bin/clang++ CACHE STRING "" FORCE)
 set(CMAKE_C_FLAGS "${cflags}" CACHE STRING "" FORCE)