Completely disable git/svn version checking if not needed.

Working with git on a branch I find it really annoying that committing
a change causes ninja to think that stuff needs to be rebuilt.

With this change at least nothing in llvm needs to be rebuild when
something is committed.

llvm-svn: 306858

llvm/CMakeLists.txt

@@ -206,7 +206,7 @@ endif()
 include(VersionFromVCS)
 
 option(LLVM_APPEND_VC_REV
-  "Append the version control system revision id to LLVM version" OFF)
+  "Embed the version control system revision id in LLVM" ON)
 
 if( LLVM_APPEND_VC_REV )
   add_version_info_from_vcs(PACKAGE_VERSION)

llvm/docs/CMake.rst

@@ -247,9 +247,10 @@ LLVM-specific variables
   tests.
 
 **LLVM_APPEND_VC_REV**:BOOL
-  Append version control revision info (svn revision number or Git revision id)
-  to LLVM version string (stored in the PACKAGE_VERSION macro). For this to work
-  cmake must be invoked before the build. Defaults to OFF.
+  Embed version control revision info (svn revision number or Git revision id).
+  This is used among other things in the LLVM version string (stored in the
+  PACKAGE_VERSION macro). For this to work cmake must be invoked before the
+  build. Defaults to ON.
 
 **LLVM_ENABLE_THREADS**:BOOL
   Build with threads support, if available. Defaults to ON.

llvm/include/llvm/Support/CMakeLists.txt

@@ -9,6 +9,7 @@ function(find_first_existing_file out_var)
 endfunction()
 
 macro(find_first_existing_vc_file out_var path)
+  if ( LLVM_APPEND_VC_REV )
     find_program(git_executable NAMES git git.exe git.cmd)
     # Run from a subdirectory to force git to print an absolute path.
     execute_process(COMMAND ${git_executable} rev-parse --git-dir
@@ -29,6 +30,7 @@ macro(find_first_existing_vc_file out_var path)
         "${path}/.svn/entries" # SVN 1.6
       )
     endif()
+  endif()
 endmacro()
 
 find_first_existing_vc_file(llvm_vc "${LLVM_MAIN_SRC_DIR}")