[Triple] Add test for if triple is RISC-V

[simoncook]

Summary

This is added as a helper/dependency for D54214, and I imagine other places will want to test for both RISC-V Triple architectures

[asb]

Thanks, added a test and applied.

include/llvm/ADT/Triple.h

bool isMIPS64() const {
     return getArch() == Triple::mips64 || getArch() == Triple::mips64el;
   }
 
   /// Tests whether the target is MIPS (little and big endian, 32- or 64-bit).
   bool isMIPS() const {
     return isMIPS32() || isMIPS64();
   }
 
+  /// Tests whether the target is RISC-V (32- and 64-bit).
+  bool isRISCV() const {
+    return getArch() == Triple::riscv32 || getArch() == Triple::riscv64;
+  }
+
   /// Tests whether the target supports comdat
   bool supportsCOMDAT() const {
     return !isOSBinFormatMachO();
   }
 
   /// Tests whether the target uses emulated TLS as default.
   bool hasDefaultEmulatedTLS() const {
     return isAndroid() || isOSOpenBSD() || isWindowsCygwinEnvironment();