snapshots of llvm build artifacts

tests/snapshot/.gitattributes

@@ -0,0 +1 @@
+snapshot.zip filter=lfs diff=lfs merge=lfs -text

tests/snapshot/.gitignore

@@ -0,0 +1,2 @@
+llvm-cmake/
+llvm-gn/

tests/snapshot/README.md

@@ -0,0 +1,34 @@
+# Snapshot tests
+
+This directory contains real-world outputs from tools that generate Ninja files.
+
+Because these outputs are large, they aren't checked in to the Ninja tree.
+Instead there is a `snapshot.zip` stored with Git LFS.  Unpack it with
+
+```
+$ unzip snapshot.zip
+```
+
+## Test data
+
+### llvm-cmake
+
+`llvm-cmake/` contains LLVM build files generated by CMake.
+
+https://llvm.org/docs/GettingStarted.html (note they have a CMake-specific page
+that has instructions that don't work(?!))
+
+```
+$ cmake -G Ninja -B build -S llvm -DCMAKE_BUILD_TYPE=Release
+```
+
+### llvm-gn
+
+`llvm-gn/` contains LLVM build files generated by the GN build system.
+
+Read llvm/utils/gn/README.rst in LLVM checkout for more, but in brief.
+
+```
+$ llvm/utils/gn/get.py
+$ llvm/utils/gn/gn.py gen out/gn
+```