[CMake] Make PAL headers copies

[CMake] Make PAL headers copies
https://bugs.webkit.org/show_bug.cgi?id=182645

Reviewed by Alex Christensen.

Source/WebCore:

No new tests. No change in behavior.

* CMakeLists.txt:

Source/WebCore/PAL:

* pal/CMakeLists.txt:
* pal/PlatformAppleWin.cmake:
* pal/PlatformGTK.cmake:
* pal/PlatformMac.cmake:
* pal/PlatformWPE.cmake:
* pal/PlatformWin.cmake:
* pal/PlatformWinCairo.cmake:

Tools:

* TestWebKitAPI/CMakeLists.txt:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@228347 268f45cc-cd09-0410-ab3c-d52691b4dbfc