[cmake] Place clang behind mlir in the list of external projects (#86050)

In preparation for the initial ClangIR upstreaming process, move clang
behind MLIR in the list of external projects. Otherwise, cmake will
attempt to build clang before MLIR.

Author: lanza

llvm/tools/CMakeLists.txt

@@ -37,11 +37,11 @@ add_llvm_tool_subdirectory(llvm-profdata)
 
 # Projects supported via LLVM_EXTERNAL_*_SOURCE_DIR need to be explicitly
 # specified.
-add_llvm_external_project(clang)
 add_llvm_external_project(lld)
 add_llvm_external_project(lldb)
 add_llvm_external_project(mlir)
-# Flang depends on mlir, so place it afterward
+# ClangIR and Flang depends on mlir, so place them afterwards
+add_llvm_external_project(clang)
 add_llvm_external_project(flang)
 add_llvm_external_project(bolt)