Removing the timestamp

Linking a program with llvm and using the -version commandline option gets output similar to the following:

LLVM version 3.7.0
DEBUG build with assertions.
Built Aug 10 2015 (04:08:22).
Default target: x86_64-pc-windows-msvc
Host CPU: sandybridge

I want to remove the time stamp on the fourth line as a step towards reproducible builds. The relevant code fragment seems to be

<< " Built " << DATE << " (" << TIME << “).\n”

so ENABLE_TIMESTAMPS needs to be set to 0 or undefined. Presumably this needs to be done during cmake, maybe as a command line parameter to same? I’ve tried “-DCMAKE_CXX_FLAGS=-DENABLE_TIMESTAMPS=0” but it doesn’t make any difference. What is the command I should be using for this?