Finally get the quoting right for both Unix and Windows for the llvmgcc and

Finally get the quoting right for both Unix and Windows for the llvmgcc and
llvmgxx programs. dejagnu doesn't understand single quote and we need to
pass double quotes through to the shell in order to escape blanks in the
paths. This patch uses \" to escape the quotes passed through to the shell.
Thanks to Aaron Gray for testing this out on cygwin.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@22155 91177308-0d34-0410-b5e6-96231b3b80d8