We need at least CMake 3.15 for dpctl-capi. (#299)

* Do not use POP_FRONT in FindDPCPP.cmake so that we can use a cmake version older that 3.15.

Author: diptorupd

dpctl-capi/cmake/modules/FindDPCPP.cmake

@@ -54,7 +54,7 @@ execute_process(
     OUTPUT_VARIABLE dpcpp_ver
 )
 
-# If dpcpp is found then set then set the package variables
+# If dpcpp is found then set the package variables
 if(${dpcpp_result} MATCHES "0")
     string(REPLACE "\n" ";" DPCPP_VERSION_LIST "${dpcpp_ver}")
     list(GET DPCPP_VERSION_LIST 0 dpcpp_ver_line)
@@ -89,7 +89,7 @@ if(${dpcpp_result} MATCHES "0")
 
     # set package-level variables
     set(DPCPP_ROOT ${DPCPP_INSTALL_DIR})
-    list(POP_FRONT DPCPP_VERSION_LIST DPCPP_VERSION)
+    list(GET DPCPP_VERSION_LIST 0 DPCPP_VERSION)
     set(DPCPP_INCLUDE_DIR ${DPCPP_INSTALL_DIR}/include)
     set(DPCPP_SYCL_INCLUDE_DIR ${DPCPP_INSTALL_DIR}/include/sycl)
     set(DPCPP_LIBRARY_DIR ${DPCPP_INSTALL_DIR}/lib)