[Sanitizer] Replace diagnostic string literal to workaround CMake 2.8 bug.

[Sanitizer] Replace diagnostic string literal to workaround CMake 2.8 bug.

Let me tell you a story. Suppose you want to build your project (e.g. LLVM)
with CMake 2.8, Clang and AddressSanitizer. You also want to ensure that
Clang is fresh enough and check that CMAKE_CXX_COMPILER_VERSION is 3.1+.
This check would fail - CMake would fail to correctly calculate compiler
version if you pass CMAKE_CXX_FLAGS=-fsanitize=address.

The problem is funky compiler version calculation in
CMakeDetermineCompilerId.cmake module: it compiles the sample source
file with provided compiler and compile flags, runs "strings" and greps
for "INFO:" ASCII strings contained on the executable to fetch
"INFO:compiler", "INFO:compiler_version" etc. It limits the output of
grep to just 4 lines.

Unfortunately, if your executable was built with ASan, it would also contain
an ASCII string
  INFO: %s ignores mlock/mlockall/munlock/munlockall
and INFO:compiler_version string would never be parsed.

All of the above actually happened after r243574 when we tried to
configure libcxx with just-built Clang with TSan/MSan, and the version
check mentioned above failed in HandleLLVMOptions.cmake

(╯°□°)╯.~.┻━┻

llvm-svn: 243599