[bazel] Add support for building lldb (llvm#87589)

This adds build configuration for building LLDB on macOS and Linux. It
uses a default subset of features that should work out of the box with
macOS + Ubuntu. It is notably missing python support right now, although
some of the scaffolding is there, because of the complexity of linking a
python dylib, especially if you plan to distribute the resulting
liblldb.so.

Most of this build file is pretty simple, one of the unfortunate
patterns I had to use was to split the header and sources cc_library
targets to break circular dependencies.

Author: keith

utils/bazel/.bazelrc

@@ -9,10 +9,16 @@
 # Prevent invalid caching if input files are modified during a build.
 build --experimental_guard_against_concurrent_changes
 
+# Automatically enable --config=(linux|macos|windows) based on the host
+build --enable_platform_specific_config
+
 # In opt mode, bazel by default builds both PIC and non-PIC object files for
 # tests vs binaries. We don't need this feature and it slows down opt builds
 # considerably.
-build --force_pic
+# TODO: Remove platform specifics we're on bazel 7.x https://github.com/bazelbuild/bazel/issues/12439
+# Apple platforms always enable pic so this flag is unnecessary anyways
+build:linux --force_pic
+build:windows --force_pic
 
 # Shared objects take up more space. With fast linkers and binaries that aren't
 # super large, the benefits of shared objects are minimal.
@@ -34,6 +40,9 @@ build --incompatible_no_implicit_file_export
 # eventually become the default
 common --incompatible_disallow_empty_glob
 
+# TODO: Remove once we move to bazel 7.x
+build --experimental_cc_shared_library
+
 ###############################################################################
 # Options to select different strategies for linking potential dependent
 # libraries. The default leaves it disabled.

utils/bazel/configure.bzl

@@ -4,8 +4,6 @@
 
 """Helper macros to configure the LLVM overlay project."""
 
-load("@bazel_tools//tools/build_defs/repo:utils.bzl", "maybe")
-
 # Directory of overlay files relative to WORKSPACE
 DEFAULT_OVERLAY_PATH = "llvm-project-overlay"
 
@@ -77,6 +75,7 @@ def _extract_cmake_settings(repository_ctx, llvm_cmake):
         "LLVM_VERSION_MAJOR": None,
         "LLVM_VERSION_MINOR": None,
         "LLVM_VERSION_PATCH": None,
+        "LLVM_VERSION_SUFFIX": None,
     }
 
     # It would be easier to use external commands like sed(1) and python.
@@ -126,6 +125,13 @@ def _extract_cmake_settings(repository_ctx, llvm_cmake):
         c["LLVM_VERSION_PATCH"],
     )
 
+    c["PACKAGE_VERSION"] = "{}.{}.{}{}".format(
+        c["LLVM_VERSION_MAJOR"],
+        c["LLVM_VERSION_MINOR"],
+        c["LLVM_VERSION_PATCH"],
+        c["LLVM_VERSION_SUFFIX"],
+    )
+
     return c
 
 def _write_dict_to_file(repository_ctx, filepath, header, vars):