CMake: target_sources() warning CMP0076

Question

I have an INTERFACE called exi and I want its INTERFACE_SOURCES to be with the source code directory during build then later during install I would copy the source files elsewhere and set INTERFACE_SOURCES to that install directory

I have the following CMakeList.txt

CMAKE_MINIMUM_REQUIRED(VERSION 3.10)
# Specify C sources and HEADER_PUBLIC directories
set(SOURCE_C
    file1.c
    file2.c
)

set(HEADER_PUBLIC
    src/header1.h
    include/header2.h    
)

#set a variable with source code install dir
set(SRC_INSTALL_DIR share/src)

#  Construct List with Full path for the build interface
set(SOURCE_C_BUILD "")
foreach(file ${SOURCE_C})
    list(APPEND SOURCE_C_BUILD "${CMAKE_CURRENT_SOURCE_DIR}/src/${file}")
endforeach()

# Construct List with Full path for the install interface
set(SOURCE_C_INSTALL "")
foreach(file ${SOURCE_C})
    list(APPEND SOURCE_C_INSTALL "${SRC_INSTALL_DIR}/${file}")
endforeach()

# Create an Interface
add_library(exi INTERFACE)

target_sources(exi INTERFACE
    $<BUILD_INTERFACE:${SOURCE_C_BUILD}>
    $<INSTALL_INTERFACE:${SOURCE_C_INSTALL}>
)

target_include_directories(exi INTERFACE
    $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
    $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/src>
    $<INSTALL_INTERFACE:include>
    $<INSTALL_INTERFACE:${SRC_INSTALL_DIR}>
)

# install source code
install(FILES ${SOURCE_C_BUILD} DESTINATION ${SRC_INSTALL_DIR})

# Install Header files
install(FILES ${HEADER_PUBLIC} DESTINATION include)

and in a higher level CMakeLists.txt exi is exported with different configs in build than install with these lines

install(
    TARGETS exi 
    EXPORT exi_targets
    DESTINATION lib/exi
)

install(EXPORT exi_targets DESTINATION lib/exi FILE exiConfig.cmake)

export(TARGETS exi FILE exiConfig.cmake)

OUTPUT

The output is correct in both exiConfig.cmake files

• build interface exiConfig.cmake

# Create imported target exi
add_library(exi INTERFACE IMPORTED)

set_target_properties(exi PROPERTIES
  INTERFACE_INCLUDE_DIRECTORIES "/workspaces/Project/inf/exi/include;/workspaces/Project/inf/exi/src"
  INTERFACE_SOURCES "/workspaces/Project/inf/exi/src/file1.c;/workspaces/Project/inf/exi/src/file2.c"
)

• install interface exiConfig.cmake

# Create imported target exi
add_library(exi INTERFACE IMPORTED)

set_target_properties(exi PROPERTIES
  INTERFACE_INCLUDE_DIRECTORIES "${_IMPORT_PREFIX}/include;${_IMPORT_PREFIX}/share/src"
  INTERFACE_SOURCES "${_IMPORT_PREFIX}/share/src/file1.c;${_IMPORT_PREFIX}/share/src/file2.c"
)

WARNING

but I am getting this warning

  Policy CMP0076 is not set: target_sources() command converts relative paths
  to absolute.  Run "cmake --help-policy CMP0076" for policy details.  Use
  the cmake_policy command to set the policy and suppress this warning.

  An interface source of target "exi" has a relative path.
This warning is for project developers.  Use -Wno-dev to suppress it.

as you can see ${SOURCE_C_BUILD} is not relative path and if I comment the line with ${SOURCE_C_INSTALL} then I would still get the same warning.