[SYCL] Use inline guarded by _WIN32 for has_extension (#16385)

I'm only able reproduce link error downstream for this API (and don't
know what exactly is causing it), but the
change is the same in nature as parts of
#16178,
#16194 and
#16267

Author: aelovikov-intel

sycl/source/backend/opencl.cpp

@@ -92,12 +92,24 @@ __SYCL_EXPORT bool has_extension(const sycl::device &SyclDevice,
 } // namespace detail
 
 #ifndef __INTEL_PREVIEW_BREAKING_CHANGES
-__SYCL_EXPORT bool has_extension(const sycl::device &SyclDevice,
-                                 const std::string &Extension) {
+// Magic combination found by trial and error:
+__SYCL_EXPORT
+#if _WIN32
+inline
+#endif
+    bool
+    has_extension(const sycl::device &SyclDevice,
+                  const std::string &Extension) {
   return detail::has_extension(SyclDevice, detail::string_view{Extension});
 }
-__SYCL_EXPORT bool has_extension(const sycl::platform &SyclPlatform,
-                                 const std::string &Extension) {
+// Magic combination found by trial and error:
+__SYCL_EXPORT
+#if _WIN32
+inline
+#endif
+    bool
+    has_extension(const sycl::platform &SyclPlatform,
+                  const std::string &Extension) {
   return detail::has_extension(SyclPlatform, detail::string_view{Extension});
 }
 #endif