[SYCL] Use relative paths for SYCL headers install (#3940)

`${SYCL_INCLUDE_DEPLOY_DIR}` is defined as
`${CMAKE_INSTALL_PREFIX}/${SYCL_INCLUDE_DIR}`, this is unnecessary
because when using relative paths, CMake will automatically prefix
install destinations with `${CMAKE_INSTALL_PREFIX}`, so we can directly
use `${SYCL_INCLUDE_DIR}`.

It is also preferable to use relative paths, because it enables the
`DESTDIR` mechanism that can make it possible to change the install
prefix after the configuration, with for example things like `make
DESTDIR=/new/install/prefix install`, or when manually calling the CMake
install scripts.

This patch has no functional changes and should have no effect on
existing builds, aside from enabling `DESTDIR`.

Author: npmiller

sycl/CMakeLists.txt

@@ -69,7 +69,6 @@ set(CLANG_VERSION "${CLANG_VERSION_MAJOR}.${CLANG_VERSION_MINOR}.${CLANG_VERSION
 
 set(SYCL_INCLUDE_DIR "include")
 set(SYCL_INCLUDE_BUILD_DIR ${LLVM_BINARY_DIR}/${SYCL_INCLUDE_DIR})
-set(SYCL_INCLUDE_DEPLOY_DIR ${CMAKE_INSTALL_PREFIX}/${SYCL_INCLUDE_DIR})
 
 add_llvm_external_project(opencl)
 list(FIND LLVM_ENABLE_PROJECTS opencl OPENCL_FOUND)
@@ -85,7 +84,7 @@ file(COPY ${OpenCL_INCLUDE_DIR}/CL
 
 # Include OpenCL Headers into final bundle.
 install(DIRECTORY ${OpenCL_INCLUDE_DIR}/CL
-        DESTINATION ${SYCL_INCLUDE_DEPLOY_DIR}/sycl
+        DESTINATION ${SYCL_INCLUDE_DIR}/sycl
         COMPONENT OpenCL-Headers)
 
 option(SYCL_BUILD_PI_CUDA
@@ -106,8 +105,8 @@ COMMAND ${CMAKE_COMMAND} -E copy_directory ${sycl_inc_dir}/CL ${SYCL_INCLUDE_BUI
 COMMENT "Copying SYCL headers ...")
 
 # Copy SYCL headers from sources to install directory
-install(DIRECTORY "${sycl_inc_dir}/sycl" DESTINATION ${SYCL_INCLUDE_DEPLOY_DIR} COMPONENT sycl-headers)
-install(DIRECTORY "${sycl_inc_dir}/CL" DESTINATION ${SYCL_INCLUDE_DEPLOY_DIR}/sycl COMPONENT sycl-headers)
+install(DIRECTORY "${sycl_inc_dir}/sycl" DESTINATION ${SYCL_INCLUDE_DIR} COMPONENT sycl-headers)
+install(DIRECTORY "${sycl_inc_dir}/CL" DESTINATION ${SYCL_INCLUDE_DIR}/sycl COMPONENT sycl-headers)
 
 set(SYCL_RT_LIBS sycl)
 if (MSVC)

sycl/test/CMakeLists.txt

@@ -8,7 +8,7 @@ set(LLVM_BUILD_BINARY_DIRS "${LLVM_BINARY_DIR}/bin/")
 set(LLVM_BUILD_LIBRARY_DIRS "${LLVM_BINARY_DIR}/lib/")
 
 set(RT_TEST_ARGS ${RT_TEST_ARGS} "-v")
-set(DEPLOY_RT_TEST_ARGS ${DEPLOY_RT_TEST_ARGS} "-v -D SYCL_TOOLS_DIR=${CMAKE_INSTALL_PREFIX}/bin -D SYCL_LIBS_DIR=${CMAKE_INSTALL_PREFIX}/lib${LLVM_LIBDIR_SUFFIX} -D SYCL_INCLUDE=${SYCL_INCLUDE_DEPLOY_DIR}")
+set(DEPLOY_RT_TEST_ARGS ${DEPLOY_RT_TEST_ARGS} "-v -D SYCL_TOOLS_DIR=${CMAKE_INSTALL_PREFIX}/bin -D SYCL_LIBS_DIR=${CMAKE_INSTALL_PREFIX}/lib${LLVM_LIBDIR_SUFFIX} -D SYCL_INCLUDE=${CMAKE_INSTALL_PREFIX}/${SYCL_INCLUDE_DIR}")
 
 find_package(Threads REQUIRED)
 set(SYCL_THREADS_LIB ${CMAKE_THREAD_LIBS_INIT})