cmake: separate generated headers from translated headers

Make a distinction between generated headers and "translated" headers.
This is important to support build-time dependencies when headers are
updated.

Generated headers are those which contain build-time feature
specifications, like `git2_features.h` that are internal to the build
and `experimental.h` that contain API information.

Translated headers are the headers that are in `include/git2`, but may
be translated to have a unique prefix like `incklude/git2-experimental`.

This distinction is important so that the CMakeFiles.txt depend on the
in-tree include files (`src/include`) and the generated header files
_but not_ the translated header files. Otherwise there are two `pack.h`
and it's unclear whether the in-tree build is targeting the one in
`src/include` or the one in the build tree.

Without this, updating an in-tree header file like `pack.h` would not
cause a rebuild of its dependencies.

deps/reftable/CMakeLists.txt

@@ -8,14 +8,12 @@ list(SORT SRC_REFTABLE)
 set_property(TARGET reftable PROPERTY C_STANDARD 99)
 target_sources(reftable PRIVATE ${SRC_REFTABLE})
 target_include_directories(reftable PRIVATE
-	include
-	"${PROJECT_BINARY_DIR}/src/util"
-	"${PROJECT_BINARY_DIR}/include"
+	"include"
 	"${PROJECT_SOURCE_DIR}/src/util"
 	"${PROJECT_SOURCE_DIR}/include"
+	"${PROJECT_BINARY_DIR}/gen_headers"
 	${LIBGIT2_DEPENDENCY_INCLUDES}
-	${LIBGIT2_SYSTEM_INCLUDES}
-)
+	${LIBGIT2_SYSTEM_INCLUDES})
 
 # The reftable library is not warning-free, so we disable turning warnings into
 # errors.

deps/xdiff/CMakeLists.txt

@@ -6,7 +6,7 @@ add_library(xdiff OBJECT ${SRC_XDIFF})
 target_include_directories(xdiff SYSTEM PRIVATE
 	"${PROJECT_SOURCE_DIR}/include"
 	"${PROJECT_SOURCE_DIR}/src/util"
-	"${PROJECT_BINARY_DIR}/src/util"
+	"${PROJECT_BINARY_DIR}/gen_headers"
 	${LIBGIT2_SYSTEM_INCLUDES}
 	${LIBGIT2_DEPENDENCY_INCLUDES})