[CMake] add public headers as INTERFACE target

include/CMakeLists.txt

@@ -176,6 +176,11 @@ set_property(TARGET freerdp APPEND PROPERTY SOURCES
     ${PUBLIC_COMMON_HEADERS}
 )
 
+add_library(freerdp-headers INTERFACE)
+target_sources(freerdp-headers INTERFACE
+	${PUBLIC_COMMON_HEADERS}
+)
+
 install(DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/freerdp
         DESTINATION ${FREERDP_INCLUDE_DIR}
         FILES_MATCHING PATTERN "*.h")

winpr/include/CMakeLists.txt

@@ -47,6 +47,11 @@ if (WITH_WINPR_TOOLS)
     )
 endif()
 
+add_library(winpr-headers INTERFACE)
+target_sources(winpr-headers INTERFACE
+	${WINPR_PUBLIC_COMMON_HEADERS}
+)
+
 install(DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/
 	DESTINATION ${WINPR_INCLUDE_DIR}
         FILES_MATCHING PATTERN "*.h")