[LLVM] Allow modulemap installation

Summary:
Currently we can't install the modulemaps provided by LLVM, since they are not structured to support headers generated as part of the build (ex. `llvm/IR/Attributes.gen`).
This patch restructures the module maps in order to support installation.

Modules containing generated headers are defined in the new `module.extern.modulemap` file, and are referenced from the main `module.modulemap` using `extern module`. There are two versions of the `module.extern.modulemap` file; one used when building and another, `module.install.modulemap`, which is re-named during installation.

Users can opt-into module map installation using `-DLLVM_INSTALL_MODULEMAPS=ON`.  The default value is `OFF` due to llvm.org/PR31905.

Reviewers: rsmith, mehdi_amini, bruno, EricWF

Reviewed By: EricWF

Subscribers: tschuett, chapuni, mgorny, llvm-commits

Differential Revision: https://reviews.llvm.org/D53510

llvm-svn: 347420

1 files changed, 5 insertions, 0 deletions

diff --git a/llvm/include/llvm/module.extern.modulemap b/llvm/include/llvm/module.extern.modulemap
new file mode 100644
index 00000000000..8acda137e04
--- /dev/null
+++ b/llvm/include/llvm/module.extern.modulemap
@@ -0,0 +1,5 @@
+module LLVM_Extern_Config_Def {}
+module LLVM_Extern_IR_Attributes_Gen {}
+module LLVM_Extern_IR_Intrinsics_Gen {}
+module LLVM_Extern_IR_Intrinsics_Enum {}
+module LLVM_Extern_Utils_DataTypes {}