cmake: improve some include related code (#680)

* cmake: avoid warning about non-existing include dir

In the Debian build logs I noticed the following warning:
cc1: warning: /build/c-ares-1.25.0/test/include: No such file or directory [-Wmissing-include-dirs]

This happened because ${CMAKE_INSTALL_INCLUDEDIR} had been added to
caresinternal. I believe it has been copied from the "real" lib
where it's used in the INSTALL_INTERFACE context. But because
caresinternal is never installed we don't need that include here.

* cmake: drop CARES_TOPLEVEL_DIR variable

The CARES_TOPLEVEL_DIR variable is the same as the automatically
created PROJECT_SOURCE_DIR variable. Let's stick to the official
one. Also because it is already used at places where CARES_TOPLEVEL_DIR
is used as well.

Fix By: Gregor Jasny (@gjasny)

CMakeLists.txt

@@ -655,10 +655,6 @@ IF (HAVE_ARPA_NAMESER_COMPAT_H)
 	SET (CARES_HAVE_ARPA_NAMESER_COMPAT_H 1)
 ENDIF()
 
-# Record toplevel CMakeLists.txt path
-set(CARES_TOPLEVEL_DIR "${CMAKE_CURRENT_SOURCE_DIR}")
-
-
 # TRANSFORM_MAKEFILE_INC
 #
 # This function consumes the "Makefile.inc" autotools file, and converts it into

src/lib/CMakeLists.txt

@@ -47,7 +47,7 @@ IF (CARES_SHARED)
 	TARGET_INCLUDE_DIRECTORIES (${PROJECT_NAME}
 		PUBLIC "$<BUILD_INTERFACE:${PROJECT_BINARY_DIR}>"
 		       "$<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}>"
-		       "$<BUILD_INTERFACE:${CARES_TOPLEVEL_DIR}/include>"
+		       "$<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>"
 		       "$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>"
 		PRIVATE "${CMAKE_CURRENT_SOURCE_DIR}"
 	)
@@ -99,7 +99,7 @@ IF (CARES_STATIC)
 	TARGET_INCLUDE_DIRECTORIES (${LIBNAME}
 		PUBLIC "$<BUILD_INTERFACE:${PROJECT_BINARY_DIR}>"
 		       "$<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}>"
-		       "$<BUILD_INTERFACE:${CARES_TOPLEVEL_DIR}/include>"
+		       "$<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>"
 		       "$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>"
 		PRIVATE "${CMAKE_CURRENT_SOURCE_DIR}"
 	)

src/tools/CMakeLists.txt

@@ -11,7 +11,7 @@ IF (CARES_BUILD_TOOLS)
 		PUBLIC "$<BUILD_INTERFACE:${PROJECT_BINARY_DIR}>"
 		       "$<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}>"
 		       "$<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/src/lib>"
-		       "$<BUILD_INTERFACE:${CARES_TOPLEVEL_DIR}/include>"
+		       "$<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>"
 		       "$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>"
 		PRIVATE "${CMAKE_CURRENT_SOURCE_DIR}"
 	)
@@ -32,7 +32,7 @@ IF (CARES_BUILD_TOOLS)
 		PUBLIC "$<BUILD_INTERFACE:${PROJECT_BINARY_DIR}>"
 		       "$<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}>"
 		       "$<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/src/lib>"
-		       "$<BUILD_INTERFACE:${CARES_TOPLEVEL_DIR}/include>"
+		       "$<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>"
 		       "$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>"
 		PRIVATE "${CMAKE_CURRENT_SOURCE_DIR}"
 	)

test/CMakeLists.txt

@@ -18,8 +18,7 @@ target_include_directories(caresinternal
              "${PROJECT_BINARY_DIR}/src/lib"
              "${PROJECT_SOURCE_DIR}"
              "${PROJECT_SOURCE_DIR}/src/lib"
-             "${CARES_TOPLEVEL_DIR}/include"
-             "${CMAKE_INSTALL_INCLUDEDIR}"
+             "${PROJECT_SOURCE_DIR}/include"
 )
 
 IF (CARES_STATIC)