[all-commits] [llvm/llvm-project] 16fef6: Fix build failure when source is read only

[pdhaliwal-amd via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 16fef6d0b46f0494c502f8fe416fe841f7b000f6
      https://github.com/llvm/llvm-project/commit/16fef6d0b46f0494c502f8fe416fe841f7b000f6
  Author: Pushpinder Singh <Pushpinder.Singh at amd.com>
  Date:   2020-05-29 (Fri, 29 May 2020)

  Changed paths:
    M llvm/cmake/modules/AddLLVM.cmake
    M llvm/include/llvm/Support/CMakeLists.txt

  Log Message:
  -----------
  Fix build failure when source is read only

cmake configure fails when it tries to setup target for llvm_vcsrevision_h
This happens only when source is checked out using repo in a read
only filesystem, because cmake tries to create `.git/logs/HEAD` file.

This patch:
  1. Recovers from failure gracefully.
  2. Ensures that VCSRevision.h is successfully created and updated
     in above scenarios.

Differential Revision: https://reviews.llvm.org/D79400