DXIL: Do not define any available runtime libcalls (#148628)

Previously this was reporting a default set of calls
as available.

Author: arsenm

llvm/include/llvm/IR/RuntimeLibcalls.td

@@ -1540,6 +1540,15 @@ def AVRSystemLibrary
               // Trigonometric rtlib functions
               avr_sin, avr_cos)>;
 
+//===----------------------------------------------------------------------===//
+// DXIL Runtime Libcalls
+//===----------------------------------------------------------------------===//
+
+def isDXIL : RuntimeLibcallPredicate<"TT.isDXIL()">;
+
+// No calls
+def DXILSystemLibrary : SystemRuntimeLibrary<isDXIL, (add)>;
+
 //===----------------------------------------------------------------------===//
 // Hexagon Runtime Libcalls
 //===----------------------------------------------------------------------===//