In CMake, prefer CMake's config headers.

Fixes #178.

Sometimes people experienced strange build problems when building
with CMake, where libpqxx seemed to be compiled for a different C++
version than the one for which it was configured.

This seems to happen in out-of-tree builds when the source tree has
the configuration headers (`include/pqxx/config-*-*.h`), generated
by the native autoconf-based build.  The CMake build would generate
similar config headers in the build tree, but when actually compiling,
the build preferred the autoconf-generated config headers over the
CMake-generated ones.

This fixes that by reordering the include directories as they are
added.

Author: jtv

NEWS

@@ -1,5 +1,6 @@
 6.4.4
  - Use pkg-config if pg-config is not available.
+ - In CMake build, prefer CMake's config headers over any found in source tree.
 6.4.3
  - Updated copyright strings.
  - Added missing "stream" headers to autotools-based install.

src/CMakeLists.txt

@@ -15,11 +15,15 @@ if(NOT PostgreSQL_INCLUDE_DIRS)
         find_package(PostgreSQL REQUIRED)
 endif()
 
+# When setting up the include paths, mention the binary tree's include
+# directory *before* the source tree's include directory.  If the source tree
+# happens to contain autoconf-generated config headers, we should still prefer
+# the ones in the binary tree.
 macro(library_target_setup tgt)
     target_include_directories(${tgt}
         PUBLIC
-            $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>
             $<BUILD_INTERFACE:${PROJECT_BINARY_DIR}/include>
+            $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>
             $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
         PRIVATE
             ${PostgreSQL_INCLUDE_DIRS}

src/CMakeLists.txt.template

@@ -2,11 +2,15 @@ if(NOT PostgreSQL_INCLUDE_DIRS)
         find_package(PostgreSQL REQUIRED)
 endif()
 
+# When setting up the include paths, mention the binary tree's include
+# directory *before* the source tree's include directory.  If the source tree
+# happens to contain autoconf-generated config headers, we should still prefer
+# the ones in the binary tree.
 macro(library_target_setup tgt)
     target_include_directories(${tgt}
         PUBLIC
-            $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>
             $<BUILD_INTERFACE:${PROJECT_BINARY_DIR}/include>
+            $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>
             $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
         PRIVATE
             ${PostgreSQL_INCLUDE_DIRS}