cmake: avoid using of pkg-config in cross-compilation mode unconditionally

- specify PKG_CONFIG_LIBDIR environment variable to new target SYSROOT

CMakeLists.txt

@@ -552,8 +552,22 @@ endif(WIN32 AND NOT MINGW)
 #       CHECK FOR SYSTEM LIBRARIES, OPTIONS, ETC..
 # ----------------------------------------------------------------------------
 if(UNIX)
-  if(NOT APPLE_FRAMEWORK)
-    find_package(PkgConfig QUIET)
+  if(NOT APPLE_FRAMEWORK OR OPENCV_ENABLE_PKG_CONFIG)
+    if(CMAKE_CROSSCOMPILING AND NOT DEFINED ENV{PKG_CONFIG_LIBDIR}
+        AND NOT OPENCV_ENABLE_PKG_CONFIG
+    )
+      if(NOT PkgConfig_FOUND)
+        message(STATUS "OpenCV disables pkg-config to avoid using of host libraries. Consider using PKG_CONFIG_LIBDIR to specify target SYSROOT")
+      elseif(OPENCV_SKIP_PKG_CONFIG_WARNING)
+        message(WARNING "pkg-config is enabled in cross-compilation mode without defining of PKG_CONFIG_LIBDIR environment variable. This may lead to misconfigured host-based dependencies.")
+      endif()
+    elseif(OPENCV_DISABLE_PKG_CONFIG)
+      if(PkgConfig_FOUND)
+        message(WARNING "OPENCV_DISABLE_PKG_CONFIG flag has no effect")
+      endif()
+    else()
+      find_package(PkgConfig QUIET)
+    endif()
   endif()
   include(CheckFunctionExists)
   include(CheckIncludeFile)