Revert "[cmake] Use `GNUInstallDirs` to support custom installation dirs."

https://lab.llvm.org/buildbot/#/builders/46/builds/21146 Still have
this odd error, not sure how to reproduce, so I will just try breaking
up my patch.

This reverts commit 4a678f8072004eff9214c1a4e1836a14abb69535.

GitOrigin-RevId: da77db58d7629a3bfea1a0053aa9c29764b0bc2b
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 340a103..33741ae 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -8,8 +8,6 @@
 
 cmake_minimum_required(VERSION 3.13.4)
 
-include(GNUInstallDirs)
-
 set(LLVM_COMMON_CMAKE_UTILS "${CMAKE_CURRENT_SOURCE_DIR}/../cmake")
 
 # Add path for custom modules
@@ -139,9 +137,9 @@
     "${CMAKE_CURRENT_SOURCE_DIR}/cmake"
     ${CMAKE_MODULE_PATH})
 
-set(LIBUNWIND_INSTALL_INCLUDE_DIR "${CMAKE_INSTALL_INCLUDEDIR}" CACHE PATH
+set(LIBUNWIND_INSTALL_INCLUDE_DIR include CACHE PATH
     "Path where built libunwind headers should be installed.")
-set(LIBUNWIND_INSTALL_RUNTIME_DIR "${CMAKE_INSTALL_BINDIR}" CACHE PATH
+set(LIBUNWIND_INSTALL_RUNTIME_DIR bin CACHE PATH
     "Path where built libunwind runtime libraries should be installed.")
 
 if(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR AND NOT APPLE)