Added cmake toolchain for RISC-V with clang.

- Added cross compile cmake file for target riscv64-clang
- Extended cmake for RISC-V and added instruction checks
- Created intrin_rvv.hpp with C++ version universal intrinsics

modules/core/src/system.cpp

@@ -399,6 +399,8 @@ struct HWFeatures
         g_hwFeatureNames[CPU_AVX512_CNL] = "AVX512-CNL";
         g_hwFeatureNames[CPU_AVX512_CLX] = "AVX512-CLX";
         g_hwFeatureNames[CPU_AVX512_ICL] = "AVX512-ICL";
+
+        g_hwFeatureNames[CPU_RVV] = "RVV";
     }
 
     void initialize(void)
@@ -597,6 +599,10 @@ struct HWFeatures
         have[CV_CPU_VSX3] = (CV_VSX3);
     #endif
 
+    #if defined __riscv && defined __riscv_vector
+        have[CV_CPU_RVV] = true;
+    #endif
+
         bool skip_baseline_check = false;
 #ifndef NO_GETENV
         if (getenv("OPENCV_SKIP_CPU_BASELINE_CHECK"))