[patch][pr17429] Do nothing in a null build if CLANG_ALWAYS_CHECK_VC_REV is OFF

[Rafael Espíndola]

Most of the time in a null build is spent checking the svn revision
number. This is very wasteful in a regular development environment.

If I understand CLANG_ALWAYS_CHECK_VC_REV correctly, it is also the
case that the version is not even always used, so we spend time for
nothing.

The attached patch moves the entire version check under
CLANG_ALWAYS_CHECK_VC_REV. On my machine that makes a null build of
bin/clang 11 times faster.

Cheers,
Rafael
-------------- next part --------------
A non-text attachment was scrubbed...
Name: t.patch
Type: application/octet-stream
Size: 1091 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20131001/dd056842/attachment.obj>