[SYCL][CMake] Apply SYCL_LIBDEVICE_CXX_FLAGS to IMF host compile (#19611)

We need to apply the custom flags both to the libdevice BC file
generation and the imf host compile, as these flags could contain paths
to stdlibc++ or glibc which are used in both.

I forgot to do this in my
[change](#19521) adding this flag.

---------

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

Author: sarnex

libdevice/cmake/modules/SYCLLibdevice.cmake

@@ -56,13 +56,18 @@ set(compile_opts
 set(SYCL_LIBDEVICE_GCC_TOOLCHAIN "" CACHE PATH "Path to GCC installation")
 
 set(SYCL_LIBDEVICE_CXX_FLAGS "" CACHE STRING "C++ compiler flags for SYCL libdevice")
+if(NOT SYCL_LIBDEVICE_CXX_FLAGS STREQUAL "")
+  separate_arguments(SYCL_LIBDEVICE_CXX_FLAGS NATIVE_COMMAND ${SYCL_LIBDEVICE_CXX_FLAGS})
+endif()
+
 if (NOT SYCL_LIBDEVICE_GCC_TOOLCHAIN STREQUAL "")
-  list(APPEND compile_opts "--gcc-install-dir=${SYCL_LIBDEVICE_GCC_TOOLCHAIN}")
+  list(APPEND SYCL_LIBDEVICE_CXX_FLAGS "--gcc-install-dir=${SYCL_LIBDEVICE_GCC_TOOLCHAIN}")
 endif()
+
 if(NOT SYCL_LIBDEVICE_CXX_FLAGS STREQUAL "")
-  separate_arguments(SYCL_LIBDEVICE_CXX_FLAGS NATIVE_COMMAND ${SYCL_LIBDEVICE_CXX_FLAGS})
   list(APPEND compile_opts ${SYCL_LIBDEVICE_CXX_FLAGS})
 endif()
+
 if(LLVM_LIBCXX_USED)
   list(APPEND compile_opts "-stdlib=libc++")
 endif()
@@ -646,12 +651,9 @@ set(imf_bf16_fallback_src ${imf_fallback_src_dir}/imf_bf16_fallback.cpp)
 set(imf_host_cxx_flags -c
   --target=${LLVM_HOST_TRIPLE}
   -D__LIBDEVICE_HOST_IMPL__
+  ${SYCL_LIBDEVICE_CXX_FLAGS}
 )
 
-if (NOT SYCL_LIBDEVICE_GCC_TOOLCHAIN STREQUAL "")
-  list(APPEND imf_host_cxx_flags "--gcc-install-dir=${SYCL_LIBDEVICE_GCC_TOOLCHAIN}")
-endif()
-
 if(LLVM_LIBCXX_USED)
   list(APPEND  imf_host_cxx_flags "-stdlib=libc++")
 endif()