CheckIncludeFiles: Honor CMAKE_REQUIRED_LIBRARIES

Other check modules honor this variable, so include file checks should
too.  Add policy `CMP0075` to enable the behavior in a compatible way.

This change was originally made by commit v3.11.0-rc1~108^2
(CheckIncludeFiles: Honor CMAKE_REQUIRED_LIBRARIES, 2017-12-24) but it
was reverted by commit v3.11.1~9^2 (Revert "CheckIncludeFiles: Honor
CMAKE_REQUIRED_LIBRARIES", 2018-04-04) because the behavior change could
affect checks in existing projects in an incompatible way.

Fixes: #9514

3 files changed, 41 insertions, 0 deletions

diff --git a/Help/manual/cmake-policies.7.rst b/Help/manual/cmake-policies.7.rst
index 7e2255d..631f75b 100644
--- a/Help/manual/cmake-policies.7.rst
+++ b/Help/manual/cmake-policies.7.rst
@@ -57,6 +57,7 @@ Policies Introduced by CMake 3.12
 .. toctree::
    :maxdepth: 1
 
+   CMP0075: Include file check macros honor CMAKE_REQUIRED_LIBRARIES. </policy/CMP0075>
    CMP0074: find_package uses PackageName_ROOT variables. </policy/CMP0074>
    CMP0073: Do not produce legacy _LIB_DEPENDS cache entries. </policy/CMP0073>
 
diff --git a/Help/policy/CMP0075.rst b/Help/policy/CMP0075.rst
new file mode 100644
index 0000000..aa5c3f7
--- /dev/null
+++ b/Help/policy/CMP0075.rst
@@ -0,0 +1,26 @@
+CMP0075
+-------
+
+Include file check macros honor ``CMAKE_REQUIRED_LIBRARIES``.
+
+In CMake 3.12 and above, the
+
+* ``check_include_file`` macro in the :module:`CheckIncludeFile` module, the
+* ``check_include_file_cxx`` macro in the
+  :module:`CheckIncludeFileCXX` module, and the
+* ``check_include_files`` macro in the :module:`CheckIncludeFiles` module
+
+now prefer to link the check executable to the libraries listed in the
+``CMAKE_REQUIRED_LIBRARIES`` variable.  This policy provides compatibility
+with projects that have not been updated to expect this behavior.
+
+The ``OLD`` behavior for this policy is to ignore ``CMAKE_REQUIRED_LIBRARIES``
+in the include file check macros.  The ``NEW`` behavior of this policy is to
+honor ``CMAKE_REQUIRED_LIBRARIES`` in the include file check macros.
+
+This policy was introduced in CMake version 3.12.  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.
+
+.. include:: DEPRECATED.txt
diff --git a/Help/release/dev/CheckIncludeFile-required-libs.rst b/Help/release/dev/CheckIncludeFile-required-libs.rst
new file mode 100644
index 0000000..6fb5c40
--- /dev/null
+++ b/Help/release/dev/CheckIncludeFile-required-libs.rst
@@ -0,0 +1,14 @@
+CheckIncludeFile-required-libs
+------------------------------
+
+* The :module:`CheckIncludeFile` module ``check_include_file`` macro
+  learned to honor the ``CMAKE_REQUIRED_LIBRARIES`` variable.
+  See policy :policy:`CMP0075`.
+
+* The :module:`CheckIncludeFileCXX` module ``check_include_file_cxx`` macro
+  learned to honor the ``CMAKE_REQUIRED_LIBRARIES`` variable.
+  See policy :policy:`CMP0075`.
+
+* The :module:`CheckIncludeFiles` module ``check_include_files`` macro
+  learned to honor the ``CMAKE_REQUIRED_LIBRARIES`` variable.
+  See policy :policy:`CMP0075`.