Export: Disallow exported interface includes in src/build tree (#14592).

Allow directories in the source tree or build tree only if the
install tree is a subdirectory of the source tree or build tree,
as appropriate.

Re-use the test files in the RunCMake.include_directories test
to run in multiple scenarios.  Bump the required CMake version
in the test to 3.0 to ensure that the new policy warnings are
emitted correctly.

Help/manual/cmake-policies.7.rst

@@ -103,3 +103,4 @@ All Policies
    /policy/CMP0049
    /policy/CMP0050
    /policy/CMP0051
+   /policy/CMP0052

Help/policy/CMP0052.rst

@@ -0,0 +1,21 @@
+CMP0052
+-------
+
+Reject source and build dirs in installed INTERFACE_INCLUDE_DIRECTORIES.
+
+CMake 3.0 and lower allowed subdirectories of the source directory or build
+directory to be in the :prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES` of
+installed and exported targets, if the directory was also a subdirectory of
+the installation prefix.  This makes the installation depend on the
+existence of the source dir or binary dir, and the installation will be
+broken if either are removed after installation.
+
+The OLD behavior for this policy is to export the content of the
+:prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES` with the source or binary
+directory.  The NEW behavior for this
+policy is to issue an error if such a directory is used.
+
+This policy was introduced in CMake version 3.1.
+CMake version |release| warns when the policy is not set and uses
+``OLD`` behavior.  Use the :command:`cmake_policy` command to set it
+to ``OLD`` or ``NEW`` explicitly.

Help/release/dev/CMP0052.rst

@@ -0,0 +1,5 @@
+CMP0052
+-------
+
+* Policy :policy:`CMP0052` introduced to control directories in the
+  :prop_tgt:`INTERFACE_INCLUDE_DIRECTORIES` of exported targets.