Use consistent casing for cmake ON/OFF flags.

No functional change. It was bothering me.

Author: vext01

.buildbot.sh

@@ -9,9 +9,9 @@ cd build
 # Disabling default PIE due to:
 # https://github.com/llvm/llvm-project/issues/57085
 cmake -DCMAKE_INSTALL_PREFIX=${INST_DIR} \
-    -DLLVM_INSTALL_UTILS=On \
+    -DLLVM_INSTALL_UTILS=ON \
     -DCMAKE_BUILD_TYPE=release \
-    -DLLVM_ENABLE_ASSERTIONS=On \
+    -DLLVM_ENABLE_ASSERTIONS=ON \
     -DLLVM_ENABLE_PROJECTS="lld;clang" \
     -DCLANG_DEFAULT_PIE_ON_LINUX=OFF \
     -DBUILD_SHARED_LIBS=ON \