[SYCL][CMake] Fix emhash build error (#19967)

We only need to link against `emhash` in build, it's an interface
library representing a header-only project (so all linking does is add
includes), and it's used internally in `xptifw` source files and in a
single non-installed header, but some other part of the code could in
theory use that non-installed header during build, so we need to link
against it, but only for build.


Manually checked the generated CMake code.


Issue introduced in #19894

Example
[error](https://github.com/intel/llvm/actions/runs/17439817298/job/49520655604?pr=19963):

```
CMake Error: install(EXPORT "unified-runtime-targets" ...) includes target "xptifw" which requires target "emhash" that is not in any export set.
```

Signed-off-by: Sarnie, Nick <[email protected]>

Author: sarnex

xptifw/src/CMakeLists.txt

@@ -67,7 +67,7 @@ function(add_xpti_library LIB_NAME)
     $<BUILD_INTERFACE:${XPTI_DIR}/include>
   )
 
-  target_link_libraries(${LIB_NAME} PUBLIC emhash::emhash)
+  target_link_libraries(${LIB_NAME} PUBLIC $<BUILD_INTERFACE:emhash::emhash>)
 
   find_package(Threads REQUIRED)
   target_link_libraries(${LIB_NAME} PUBLIC ${CMAKE_DL_LIBS} Threads::Threads)