[llvm] [CMake] Fix config when static zstd libraries are not found (PR #113584)

[Aaron Puchert via llvm-commits]

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@@ -196,7 +196,18 @@ if(LLVM_ENABLE_ZSTD)
     find_package(zstd QUIET)
   endif()
 endif()
-set(LLVM_ENABLE_ZSTD ${zstd_FOUND})
+
+# If LLVM_USE_STATIC_ZSTD is specified, make sure we enable zstd only if static
+# libraries are found.
+if(LLVM_USE_STATIC_ZSTD AND NOT TARGET zstd::libzstd_static)
+  # Fail if LLVM_ENABLE_ZSTD is FORCE_ON.
+  if(LLVM_ENABLE_ZSTD STREQUAL FORCE_ON)
+      message(FATAL_ERROR "Failed to find static zstd libraries, but LLVM_USE_STATIC_ZSTD=ON and LLVM_ENABLE_ZSTD=FORCE_ON.")
+  endif()
+  set(LLVM_ENABLE_ZSTD OFF)
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aaronpuchert wrote:

Is that relevant when you're emitting a fatal error anyway?

https://github.com/llvm/llvm-project/pull/113584