[cmake] Add missing CMakePushCheckState include to FindLibEdit.cmake

Add the missing include to fix an error when `cmake_push_check_state()`
is called and incidentally the CMakePushCheckState module is not loaded
by any other check running prior to `FindLibEdit.cmake`:

    CMake Error at /var/no-tmpfs/portage/dev-util/lldb-15.0.4/work/cmake/Modules/FindLibEdit.cmake:24 (cmake_push_check_state):
      Unknown CMake command "cmake_push_check_state".
    Call Stack (most recent call first):
      cmake/modules/LLDBConfig.cmake:52 (find_package)
      cmake/modules/LLDBConfig.cmake:59 (add_optional_dependency)
      CMakeLists.txt:28 (include)

Gentoo Bug: https://bugs.gentoo.org/880065

Differential Revision: https://reviews.llvm.org/D137555

(cherry picked from commit 3676a86)

Author: mgorny

cmake/Modules/FindLibEdit.cmake

@@ -21,6 +21,7 @@ find_library(LibEdit_LIBRARIES NAMES edit HINTS ${PC_LIBEDIT_LIBRARY_DIRS})
 
 include(CheckIncludeFile)
 if(LibEdit_INCLUDE_DIRS AND EXISTS "${LibEdit_INCLUDE_DIRS}/histedit.h")
+  include(CMakePushCheckState)
   cmake_push_check_state()
   list(APPEND CMAKE_REQUIRED_INCLUDES ${LibEdit_INCLUDE_DIRS})
   list(APPEND CMAKE_REQUIRED_LIBRARIES ${LibEdit_LIBRARIES})