[Clang][SPIRV][AMDGPU] Override supportsLibCall for AMDGCNSPIRV (#143814)

The `supportsLibCall` predicate is used to select whether some math builtins get expanded in the FE or they get lowered into libcalls. The default implementation unconditionally returns true, which is problematic for AMDGCN-flavoured SPIRV, as AMDGPU does not support any libcalls at the moment. This change overrides the predicate in order to reflect this and correctly do the expected FE expansion when targeting AMDGCN-flavoured SPIRV.

Author: AlexVlx

clang/lib/CodeGen/Targets/SPIR.cpp

@@ -75,6 +75,10 @@ class SPIRVTargetCodeGenInfo : public CommonSPIRTargetCodeGenInfo {
                                          SyncScope Scope,
                                          llvm::AtomicOrdering Ordering,
                                          llvm::LLVMContext &Ctx) const override;
+  bool supportsLibCall() const override {
+    return getABIInfo().getTarget().getTriple().getVendor() !=
+           llvm::Triple::AMD;
+  }
 };
 
 inline StringRef mapClangSyncScopeToLLVM(SyncScope Scope) {