[CMake] Quote variables where "TARGET" may be a value

[thesamesam]

Summary

In CMake, "TARGET" is a special keyword. But it's also an LLVM component, which
means downstreams may request "target" or "TARGET" from CMake. Quote such input
so "TARGET" is interpreted as a string rather than a keyword.

This is a followup to 75a0502fe0053c72b57b61143a55600814d931fd (D150884).

Fixes Meson's test suite and an issue which manifested identically to #61436
but appears to have been a slightly different problem.

Bug: https://github.com/mesonbuild/meson/issues/11642
Bug: https://github.com/llvm/llvm-project/issues/61436

[thesamesam]

Tweak commit message

[thesamesam]

Add some additional cases

[tstellar]

LGTM.

llvm/cmake/modules/LLVM-Config.cmake

 function(llvm_expand_pseudo_components out_components)
   set( link_components ${ARGN} )
   if(NOT LLVM_AVAILABLE_LIBS)
     # Inside LLVM itself available libs are in a global property.
     get_property(LLVM_AVAILABLE_LIBS GLOBAL PROPERTY LLVM_LIBS)
   endif()
   foreach(c ${link_components})
     # add codegen, asmprinter, asmparser, disassembler
-    if(${c} IN_LIST LLVM_TARGETS_TO_BUILD)
+    if("${c}" IN_LIST LLVM_TARGETS_TO_BUILD)
       if(LLVM${c}CodeGen IN_LIST LLVM_AVAILABLE_LIBS)
         list(APPEND expanded_components "${c}CodeGen")
       else()
         if(LLVM${c} IN_LIST LLVM_AVAILABLE_LIBS)
           list(APPEND expanded_components "${c}")
         else()
           message(FATAL_ERROR "Target ${c} is not in the set of libraries.")
         endif()
       endif()
       foreach(subcomponent IN ITEMS AsmPrinter AsmParser Desc Disassembler Info Utils)
         if(LLVM${c}${subcomponent} IN_LIST LLVM_AVAILABLE_LIBS)
           list(APPEND expanded_components "${c}${subcomponent}")
         endif()
       endforeach()
-    elseif( c STREQUAL "nativecodegen" )
+    elseif("${c}" STREQUAL "nativecodegen" )
       foreach(subcomponent IN ITEMS CodeGen Desc Info)
         if(LLVM${LLVM_NATIVE_ARCH}${subcomponent} IN_LIST LLVM_AVAILABLE_LIBS)
           list(APPEND expanded_components "${LLVM_NATIVE_ARCH}${subcomponent}")
         endif()
       endforeach()
-    elseif( c STREQUAL "AllTargetsCodeGens" )
+    elseif("${c}" STREQUAL "AllTargetsCodeGens" )
       # Link all the codegens from all the targets
       foreach(t ${LLVM_TARGETS_TO_BUILD})
         if( TARGET LLVM${t}CodeGen)
           list(APPEND expanded_components "${t}CodeGen")
         endif()
       endforeach(t)
-    elseif( c STREQUAL "AllTargetsAsmParsers" )
+    elseif("${c}" STREQUAL "AllTargetsAsmParsers" )
       # Link all the asm parsers from all the targets
       foreach(t ${LLVM_TARGETS_TO_BUILD})
         if(LLVM${t}AsmParser IN_LIST LLVM_AVAILABLE_LIBS)
           list(APPEND expanded_components "${t}AsmParser")
         endif()
       endforeach(t)
-    elseif( c STREQUAL "AllTargetsDescs" )
+    elseif( "${c}" STREQUAL "AllTargetsDescs" )
       # Link all the descs from all the targets
       foreach(t ${LLVM_TARGETS_TO_BUILD})
         if(LLVM${t}Desc IN_LIST LLVM_AVAILABLE_LIBS)
           list(APPEND expanded_components "${t}Desc")
         endif()
       endforeach(t)
-    elseif( c STREQUAL "AllTargetsDisassemblers" )
+    elseif("${c}" STREQUAL "AllTargetsDisassemblers" )
       # Link all the disassemblers from all the targets
       foreach(t ${LLVM_TARGETS_TO_BUILD})
         if(LLVM${t}Disassembler IN_LIST LLVM_AVAILABLE_LIBS)
           list(APPEND expanded_components "${t}Disassembler")
         endif()
       endforeach(t)
-    elseif( c STREQUAL "AllTargetsInfos" )
+    elseif("${c}" STREQUAL "AllTargetsInfos" )
       # Link all the infos from all the targets
       foreach(t ${LLVM_TARGETS_TO_BUILD})
         if(LLVM${t}Info IN_LIST LLVM_AVAILABLE_LIBS)
           list(APPEND expanded_components "${t}Info")
         endif()
       endforeach(t)
-    elseif( c STREQUAL "AllTargetsMCAs" )
+    elseif("${c}" STREQUAL "AllTargetsMCAs" )
       # Link all the TargetMCAs from all the targets
       foreach(t ${LLVM_TARGETS_TO_BUILD})
         if( TARGET LLVM${t}TargetMCA )
           list(APPEND expanded_components "${t}TargetMCA")
         endif()
       endforeach(t)
     else()
       list(APPEND expanded_components "${c}")
function(llvm_map_components_to_libnames out_libs)
   get_property(LLVM_TARGETS_CONFIGURED GLOBAL PROPERTY LLVM_TARGETS_CONFIGURED)
 
   # Generally in our build system we avoid order-dependence. Unfortunately since
   # not all targets create the same set of libraries we actually need to ensure
   # that all build targets associated with a target are added before we can
   # process target dependencies.
   if(NOT LLVM_TARGETS_CONFIGURED)
     foreach(c ${link_components})
-      is_llvm_target_specifier(${c} iltl_result ALL_TARGETS)
+      is_llvm_target_specifier("${c}" iltl_result ALL_TARGETS)
       if(iltl_result)
         message(FATAL_ERROR "Specified target library before target registration is complete.")
       endif()
     endforeach()
   endif()
 
   # Expand some keywords:
   if(engine IN_LIST link_components)
function(llvm_map_components_to_libnames out_libs)
 
   # Translate symbolic component names to real libraries:
   llvm_expand_pseudo_components(link_components ${link_components})
   foreach(c ${link_components})
     get_property(c_rename GLOBAL PROPERTY LLVM_COMPONENT_NAME_${c})
     if(c_rename)
         set(c ${c_rename})
     endif()
-    if( c STREQUAL "native" )
+    if("${c}" STREQUAL "native" )
       # already processed
-    elseif( c STREQUAL "backend" )
+    elseif("${c}" STREQUAL "backend" )
       # same case as in `native'.
-    elseif( c STREQUAL "engine" )
+    elseif("${c}" STREQUAL "engine" )
       # already processed
-    elseif( c STREQUAL "all" )
+    elseif("${c}" STREQUAL "all" )
       get_property(all_components GLOBAL PROPERTY LLVM_COMPONENT_LIBS)
       list(APPEND expanded_components ${all_components})
     else()
       # Canonize the component name:
       string(TOUPPER "${c}" capitalized)
       list(FIND capitalized_libs LLVM${capitalized} lib_idx)
       if( lib_idx LESS 0 )
         # The component is unknown. Maybe is an omitted target?
-        is_llvm_target_library(${c} iltl_result OMITTED_TARGETS)
+        is_llvm_target_library("${c}" iltl_result OMITTED_TARGETS)
         if(iltl_result)
           # A missing library to a directly referenced omitted target would be bad.
           message(FATAL_ERROR "Library '${c}' is a direct reference to a target library for an omitted target.")
         else()
           # If it is not an omitted target we should assume it is a component
           # that hasn't yet been processed by CMake. Missing components will
           # cause errors later in the configuration, so we can safely assume
           # that this is valid here.
           list(APPEND expanded_components LLVM${c})
         endif()
       else( lib_idx LESS 0 )
         list(GET LLVM_AVAILABLE_LIBS ${lib_idx} canonical_lib)
         list(APPEND expanded_components ${canonical_lib})
       endif( lib_idx LESS 0 )
-    endif( c STREQUAL "native" )
+    endif("${c}" STREQUAL "native" )
   endforeach(c)
 
   set(${out_libs} ${expanded_components} PARENT_SCOPE)
 endfunction()
 
 # Perform a post-order traversal of the dependency graph.
 # This duplicates the algorithm used by llvm-config, originally
 # in tools/llvm-config/llvm-config.cpp, function ComputeLibsForComponents.