Revert "Revert "Revert "Use `GNUInstallDirs` to support custom installation dirs. -- LLVM"""

This reverts commit 492de35df443d5f31480173d5f1274c7835cd3d8.

I tried to apply John's changes in 8d897ec91528 that were expected to
fix his patch but that didn't work unfortunately.

Reverting this again to fix the macOS bots and leave him more time to
investigate the issue.

GitOrigin-RevId: 30fc88bf1dc15a72e2d9809d28019d386b7a7cc0
diff --git a/CMakeLists.txt b/CMakeLists.txt
index e90e0fd..ec39ea6 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -183,8 +183,8 @@
 
 # pkg-config file
 configure_file( libclc.pc.in libclc.pc @ONLY )
-install( FILES ${CMAKE_CURRENT_BINARY_DIR}/libclc.pc DESTINATION "${CMAKE_INSTALL_DATADIR}/pkgconfig" )
-install( DIRECTORY generic/include/clc DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}" )
+install( FILES ${CMAKE_CURRENT_BINARY_DIR}/libclc.pc DESTINATION ${CMAKE_INSTALL_DATADIR}/pkgconfig )
+install( DIRECTORY generic/include/clc DESTINATION ${CMAKE_INSTALL_INCLUDEDIR} )
 
 if( ENABLE_RUNTIME_SUBNORMAL )
 	add_library( subnormal_use_default STATIC
@@ -192,7 +192,7 @@
 	add_library( subnormal_disable STATIC
 		generic/lib/subnormal_disable.ll )
 	install( TARGETS subnormal_use_default subnormal_disable ARCHIVE
-		DESTINATION "${CMAKE_INSTALL_DATADIR}/clc" )
+		DESTINATION ${CMAKE_INSTALL_DATADIR}/clc )
 endif()
 
 find_package( Python3 REQUIRED COMPONENTS Interpreter )
@@ -343,7 +343,7 @@
 			add_custom_target( "prepare-${spv_suffix}" ALL
 			                   DEPENDS "${spv_suffix}" )
 			install( FILES ${CMAKE_CURRENT_BINARY_DIR}/${spv_suffix}
-				 DESTINATION "${CMAKE_INSTALL_DATADIR}/clc" )
+				 DESTINATION ${CMAKE_INSTALL_DATADIR}/clc )
 		else()
 
 			# Add prepare target
@@ -366,7 +366,7 @@
 					PROPERTIES ENVIRONMENT "LLVM_CONFIG=${LLVM_CONFIG}" )
 			endif()
 
-			install( FILES ${CMAKE_CURRENT_BINARY_DIR}/${obj_suffix} DESTINATION "${CMAKE_INSTALL_DATADIR}/clc" )
+			install( FILES ${CMAKE_CURRENT_BINARY_DIR}/${obj_suffix} DESTINATION ${CMAKE_INSTALL_DATADIR}/clc )
 			foreach( a ${${d}_aliases} )
 				set( alias_suffix "${a}-${t}.bc" )
 				add_custom_target( ${alias_suffix} ALL
@@ -374,7 +374,7 @@
 						   create_symlink ${obj_suffix}
 						   ${alias_suffix}
 				                   DEPENDS "prepare-${obj_suffix}" )
-				install( FILES ${CMAKE_CURRENT_BINARY_DIR}/${alias_suffix} DESTINATION "${CMAKE_INSTALL_DATADIR}/clc" )
+				install( FILES ${CMAKE_CURRENT_BINARY_DIR}/${alias_suffix} DESTINATION ${CMAKE_INSTALL_DATADIR}/clc )
 			endforeach( a )
 		endif()
 	endforeach( d )