fix(cmake): generate version.h under PROJECT_BINARY_DIR to support add_subdirectory() builds (#906)

CMakeLists.txt generates the versioned header at
${CMAKE_BINARY_DIR}/src/iceberg/version.h, but the include path used
to compile the iceberg target (ICEBERG_INCLUDES in
src/iceberg/CMakeLists.txt) is ${PROJECT_BINARY_DIR}/src. This change
makes both consistently use PROJECT_BINARY_DIR.

When iceberg-cpp is built as the top-level project, CMAKE_BINARY_DIR
and PROJECT_BINARY_DIR happen to be the same directory, so this
mismatch is invisible.

When iceberg-cpp is consumed via add_subdirectory() from another
CMake project (e.g. vendoring it under third/iceberg-cpp/),
CMAKE_BINARY_DIR resolves to the outermost project's build directory,
while PROJECT_BINARY_DIR correctly resolves to the build directory
nested under the outer project (e.g.
<outer_build_dir>/third/iceberg-cpp/). The generated version.h then
ends up in the wrong place and any translation unit that does
#include "iceberg/version.h" (e.g. catalog/rest/constant.h,
deletes/dv_util.cc, deletes/dv_writer.cc) fails with a missing header
when building as a nested dependency.

Co-authored-by: joeyyjwang <joeyyjwang@tencent.com>

Author: Angelia-Wang

CMakeLists.txt

@@ -30,7 +30,7 @@ project(Iceberg
 
 include(IcebergBuildUtils)
 iceberg_configure_version_header("${CMAKE_CURRENT_SOURCE_DIR}/src/iceberg/version.h.in"
-                                 "${CMAKE_BINARY_DIR}/src/iceberg/version.h")
+                                 "${PROJECT_BINARY_DIR}/src/iceberg/version.h")
 
 set(CMAKE_CXX_STANDARD 23)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)