[clang][cmake] Use `GNUInstallDirs` to support custom installation dirs

I am breaking apart D99484 so the cause of build failures is easier to
understand.

Differential Revision: https://reviews.llvm.org/D117419

NOKEYCHECK=True
GitOrigin-RevId: 10d0d8c0c1db57b7ff465df7ced78a42a20d592d
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 35ecdb1..bbdef93 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -21,20 +21,20 @@
 endif()
 
 install(PROGRAMS clang-format-bbedit.applescript
-  DESTINATION share/clang
+  DESTINATION "${CMAKE_INSTALL_DATADIR}/clang"
   COMPONENT clang-format)
 install(PROGRAMS clang-format-diff.py
-  DESTINATION share/clang
+  DESTINATION "${CMAKE_INSTALL_DATADIR}/clang"
   COMPONENT clang-format)
 install(PROGRAMS clang-format-sublime.py
-  DESTINATION share/clang
+  DESTINATION "${CMAKE_INSTALL_DATADIR}/clang"
   COMPONENT clang-format)
 install(PROGRAMS clang-format.el
-  DESTINATION share/clang
+  DESTINATION "${CMAKE_INSTALL_DATADIR}/clang"
   COMPONENT clang-format)
 install(PROGRAMS clang-format.py
-  DESTINATION share/clang
+  DESTINATION "${CMAKE_INSTALL_DATADIR}/clang"
   COMPONENT clang-format)
 install(PROGRAMS git-clang-format
-  DESTINATION bin
+  DESTINATION "${CMAKE_INSTALL_BINDIR}"
   COMPONENT clang-format)