[SYCL] Fix overloadble requirement for sycl_device_only

Author: npmiller

clang/lib/Sema/SemaDecl.cpp

@@ -7355,6 +7355,10 @@ static bool isIncompleteDeclExternC(Sema &S, const T *D) {
     if (S.getLangOpts().CUDA && (D->template hasAttr<CUDADeviceAttr>() ||
                                  D->template hasAttr<CUDAHostAttr>()))
       return false;
+
+    // So does SYCL's device_only attribute.
+    if (S.getLangOpts().isSYCL() && D->template hasAttr<SYCLDeviceOnlyAttr>())
+      return false;
   }
   return D->isExternC();
 }

sycl/include/sycl/stl_wrappers/cmath-fallback.h

@@ -3,10 +3,9 @@
 
 #ifdef __SYCL_DEVICE_ONLY__
 
-#define __DPCPP_SYCL_DEVICE                                                    \
-  __attribute__((sycl_device_only, always_inline, overloadable))
+#define __DPCPP_SYCL_DEVICE __attribute__((sycl_device_only, always_inline))
 #define __DPCPP_SYCL_DEVICE_C                                                  \
-  extern "C" __attribute__((sycl_device_only, always_inline, overloadable))
+  extern "C" __attribute__((sycl_device_only, always_inline))
 
 #define __DPCPP_SPIRV_MAP_UNARY(NAME)                                          \
   __DPCPP_SYCL_DEVICE_C float NAME##f(float x) {                               \