[pdb] Fix linker module symbols to work with dbgeng.

The linker module contains a symbol of type S_COMPILE3 which
contains various information about the compiler and linker used
to create the PDB, such as the name of the linker, the target
machine, and the linker version.  Interestingly, if we set the
version string to 0.0.0.0, then when trying to view local
variables WinDbg emits an error that private symbols are not
present.  By setting this to a valid MSVC linker version string,
local variables can display.

As such, even though it is not representative of LLVM's version
information, we need this for compatibility.

llvm-svn: 310755