Update compiler extension integration into the build system

The approach here is to create a new (empty) component, `Extensions', where all
statically compiled extensions dynamically register their dependencies. That way
we're more natively compatible with LLVMBuild and llvm-config.

Fixes: https://bugs.llvm.org/show_bug.cgi?id=44870

Differential Revision: https://reviews.llvm.org/D78192

(cherry picked from commit 8f766e382b77eef3102798b49e087d1e4804b984)

3 files changed, 24 insertions, 0 deletions

diff --git a/llvm/lib/Extensions/CMakeLists.txt b/llvm/lib/Extensions/CMakeLists.txt
new file mode 100644
index 00000000000..701e9c4c0ba
--- /dev/null
+++ b/llvm/lib/Extensions/CMakeLists.txt
@@ -0,0 +1,3 @@
+add_llvm_component_library(LLVMExtensions
+    Extensions.cpp
+)
diff --git a/llvm/lib/Extensions/Extensions.cpp b/llvm/lib/Extensions/Extensions.cpp
new file mode 100644
index 00000000000..e69de29bb2d
--- /dev/null
+++ b/llvm/lib/Extensions/Extensions.cpp
diff --git a/llvm/lib/Extensions/LLVMBuild.txt b/llvm/lib/Extensions/LLVMBuild.txt
new file mode 100644
index 00000000000..2005830a4dd
--- /dev/null
+++ b/llvm/lib/Extensions/LLVMBuild.txt
@@ -0,0 +1,21 @@
+;===- ./lib/Extensions/LLVMBuild.txt -------------------------------*- Conf -*--===;
+;
+; Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+; See https://llvm.org/LICENSE.txt for license information.
+; SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+;
+;===------------------------------------------------------------------------===;
+;
+; This is an LLVMBuild description file for the components in this subdirectory.
+;
+; For more information on the LLVMBuild system, please see:
+;
+;   http://llvm.org/docs/LLVMBuild.html
+;
+;===------------------------------------------------------------------------===;
+
+[component_0]
+type = Library
+name = Extensions
+parent = Libraries
+required_libraries =