llvm: convert bitcode in static archives to object code

In #106925, I enabled LTO for our LLVM build. This creates static
archives that contain LLVM bitcode instead of object code. This makes
the static archives more difficult to use, requiring workarounds such as

    https://github.com/Homebrew/homebrew-core/blob/c01f1794fc3decce04b71cae03966213fc7af34d/Formula/enzyme.rb#L30

and has caused problems for multiple downstream projects.

We can fix this by converting the bitcode into object code, which is
what Fedora does with their LLVM build. They also build their toolchain
with LTO.

Alternatively, we can disable LTO, but that foregoes significant
speedups we get from enabling it.

While we're here, let's add some test coverage for features that were
recently enabled that we don't test.

Fixes:

ziglang/zig#12923
halide/Halide#7055
mesonbuild/meson#10879
Homebrew/discussions#3666

Formula/llvm.rb

@@ -432,6 +432,24 @@ def install
 
     # Install Emacs modes
     elisp.install llvmpath.glob("utils/emacs/*.el") + share.glob("clang/*.el")
+
+    return if OS.linux? || !pgo_build
+
+    # Convert LTO-generated bitcode in our static archives to MachO. Adapted from Fedora:
+    # https://src.fedoraproject.org/rpms/redhat-rpm-config/blob/rawhide/f/brp-llvm-compile-lto-elf
+    lib.glob("*.a").each do |static_archive|
+      mktemp do
+        system bin/"llvm-ar", "x", static_archive
+        Pathname.glob("*.o").each do |bc_file|
+          file_type = Utils.safe_popen_read("file", bc_file)
+          next unless file_type.match?("LLVM bitcode")
+
+          system bin/"clang", "-fno-lto", "-Wno-unused-command-line-argument",
+                              "-x", "ir", bc_file, "-c", "-o", bc_file
+          system bin/"llvm-ar", "r", static_archive, bc_file
+        end
+      end
+    end
   end
 
   def caveats
@@ -643,6 +661,17 @@ def caveats
     assert_equal "int main() { printf(\"Hello world!\"); }\n",
       shell_output("#{bin}/clang-format -style=google clangformattest.c")
 
+    # Test static analyzer
+    (testpath/"unreachable.c").write <<~EOS
+      unsigned int func(unsigned int a) {
+        unsigned int *z = 0;
+        if ((a & 1) && ((a & 1) ^1))
+          return *z; // unreachable
+        return 0;
+      }
+    EOS
+    system bin/"clang", "--analyze", "-Xanalyzer", "-analyzer-constraints=z3", "unreachable.c"
+
     # This will fail if the clang bindings cannot find `libclang`.
     with_env(PYTHONPATH: prefix/Language::Python.site_packages(python3)) do
       system python3, "-c", <<~EOS
@@ -651,6 +680,10 @@ def caveats
       EOS
     end
 
+    # Check that lldb can use Python
+    lldb_script_interpreter_info = JSON.parse(shell_output("#{bin}/lldb --print-script-interpreter-info"))
+    assert_equal "python", lldb_script_interpreter_info["language"]
+
     # Ensure LLVM did not regress output of `llvm-config --system-libs` which for a time
     # was known to output incorrect linker flags; e.g., `-llibxml2.tbd` instead of `-lxml2`.
     # On the other hand, note that a fully qualified path to `dylib` or `tbd` is OK, e.g.,