Fix ttmlir-(opt/translate) linking to llvm dylib (again) (#1621)

I seem to have accidentally changed `DMLIR_LINK_MLIR_DYLIB` instead of
`DLLVM_LINK_LLVM_DYLIB` last time 🤦
And must not have properly cleared all build files when I tested, s.t.
it picked up manual fix previously with correct variable change.
Correcting here--planning to leave change to `DMLIR_LINK_MLIR_DYLIB=OFF`
too, for symmetry

env/CMakeLists.txt

@@ -52,7 +52,7 @@ ExternalProject_Add(
     -DLLVM_ENABLE_PIC=ON
     -DLLVM_BUILD_LLVM_DYLIB=ON
     -DLLVM_INSTALL_GTEST=ON
-    -DLLVM_LINK_LLVM_DYLIB=ON
+    -DLLVM_LINK_LLVM_DYLIB=OFF
     -DMLIR_BUILD_MLIR_C_DYLIB=ON
     -DMLIR_LINK_MLIR_DYLIB=OFF
     -DMLIR_BUILD_MLIR_C_DYLIB=ON