ExternalProject: Avoid unnecessary checkout on clone
The clone step checks out the cloned branch but is always followed by an
explicit checkout of the desired `GIT_TAG`. Tell `git clone` not to
check out.
diff --git a/Modules/ExternalProject.cmake b/Modules/ExternalProject.cmake
index 14fc231..e55ed46 100644
--- a/Modules/ExternalProject.cmake
+++ b/Modules/ExternalProject.cmake
@@ -1079,7 +1079,7 @@
message(FATAL_ERROR "Tag for git checkout should not be empty.")
endif()
- set(git_clone_options)
+ set(git_clone_options "--no-checkout")
if(git_shallow)
if(NOT GIT_VERSION_STRING VERSION_LESS 1.7.10)
list(APPEND git_clone_options "--depth 1 --no-single-branch")
