[llvm] [test] Add missing canonicalization of LLVM_ENABLE_ZSTD

Add LLVM_ENABLE_ZSTD to llvm_canonicalize_cmake_booleans().  This is
needed to ensure that the substitutions in lit.site.cfg.py resolve
to correct Python booleans.

Differential Revision: https://reviews.llvm.org/D135357

(cherry picked from commit bc4bcbc)

Author: mgorny

llvm/test/CMakeLists.txt

@@ -8,6 +8,7 @@ llvm_canonicalize_cmake_booleans(
   LLVM_ENABLE_CURL
   LLVM_ENABLE_HTTPLIB
   LLVM_ENABLE_ZLIB
+  LLVM_ENABLE_ZSTD
   LLVM_ENABLE_LIBXML2
   LLVM_INCLUDE_GO_TESTS
   LLVM_LINK_LLVM_DYLIB