[llvm] Escape LLVM_TARGETS_TO_BUILD while checking against LLVM_ALL_TARGETS and LLVM_EXPERIMENTAL_TARGETS_TO_BUILD (PR #70885)

[Shoaib Meenai via llvm-commits]

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@@ -942,7 +942,7 @@ foreach(t ${LLVM_TARGETS_TO_BUILD})
   # LLVM_EXPERIMENTAL_TARGETS_TO_BUILD, not LLVM_TARGETS_TO_BUILD.
   # We allow experimental targets that are not in LLVM_ALL_EXPERIMENTAL_TARGETS,
   # as long as they are passed via LLVM_EXPERIMENTAL_TARGETS_TO_BUILD.
-  if ( NOT ${t} IN_LIST LLVM_ALL_TARGETS AND NOT ${t} IN_LIST LLVM_EXPERIMENTAL_TARGETS_TO_BUILD )
+  if ( NOT "${t}" IN_LIST LLVM_ALL_TARGETS AND NOT "${t}" IN_LIST LLVM_EXPERIMENTAL_TARGETS_TO_BUILD )
     if( ${t} IN_LIST LLVM_ALL_EXPERIMENTAL_TARGETS )
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smeenai wrote:

```suggestion
    if( "${t}" IN_LIST LLVM_ALL_EXPERIMENTAL_TARGETS )
```

https://github.com/llvm/llvm-project/pull/70885