[clang] [llvm] test-release.sh: Add a CMake cache file for 3-stage release builds (PR #75903)

[Konrad Kleine via cfe-commits]

================
@@ -0,0 +1,41 @@
+# Plain options configure the first build.
+# BOOTSTRAP_* options configure the second build.
+# BOOTSTRAP_BOOTSTRAP_* options configure the third build.
+
+set(CMAKE_BUILD_TYPE RELEASE CACHE STRING "")
+
+# Stage 1 Bootstrap Setup
+set(CLANG_ENABLE_BOOTSTRAP ON CACHE BOOL "")
+set(CLANG_BOOTSTRAP_TARGETS
+  clang
+  check-all
+  check-llvm
+  check-clang
+  test-suite
+  stage3
+  stage3-clang
+  stage3-check-all
+  stage3-check-llvm
+  stage3-check-clang
+  stage3-install
+  stage3-test-suite CACHE STRING "")
+
+# Stage 1 Options
+set(LLVM_ENABLE_PROJECTS "clang" CACHE STRING "")
+set(LLVM_TARGETS_TO_BUILD Native CACHE STRING "")
+
+# Stage 2 Bootstrap Setup
+set(BOOTSTRAP_CLANG_ENABLE_BOOTSTRAP=ON CACHE STRING "")
----------------
kwk wrote:

```suggestion
set(BOOTSTRAP_CLANG_ENABLE_BOOTSTRAP ON CACHE STRING "")
```

We don't need the additional `=`, do we @tstellar  ?

https://github.com/llvm/llvm-project/pull/75903