Add Triple::isAMDGPU

[yaxunl]

Summary

I have been bothered by missing Triple::isAMDGPU for long time. There is isNVPTX, isARM,
why can't we have isAMDGPU?

[rampitec]

LGTM

[arsenm]

Needs unit test

[yaxunl]

add usage of it

[yaxunl]

In D57707#1383819, @arsenm wrote:

Needs unit test

I used it in TargetLibraryInfo.cpp. We have lit tests cover them, so they also cover this function.

include/llvm/ADT/Triple.h

return getEnvironment() == Triple::Musl ||
            getEnvironment() == Triple::MuslEABIHF;
   }
 
   /// Tests whether the target is NVPTX (32- or 64-bit).
   bool isNVPTX() const {
     return getArch() == Triple::nvptx || getArch() == Triple::nvptx64;
   }
 
+  bool isAMDGPU() const {
+    return getArch() == Triple::r600 || getArch() == Triple::amdgcn;
+  }
+
   /// Tests whether the target is Thumb (little and big endian).
   bool isThumb() const {
     return getArch() == Triple::thumb || getArch() == Triple::thumbeb;
   }
 
   /// Tests whether the target is ARM (little and big endian).
   bool isARM() const {
     return getArch() == Triple::arm || getArch() == Triple::armeb;