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

This reverts commit 797b50d4be873b4662983413a06806fca544c276.

See the original D99484. @mib who noticed the original problem could not longer
reproduce it, after I tried and also failed. We are threfore hoping it went
away on its own!

Reviewed By: mib

Differential Revision: https://reviews.llvm.org/D115544

GitOrigin-RevId: 492de35df443d5f31480173d5f1274c7835cd3d8
diff --git a/CMakeLists.txt b/CMakeLists.txt
index ec39ea6..e90e0fd 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 )