Fix regular expression used by 'make update' to only look for 'I' and '?' at the start of svn info results and to check for spaces after 'I' instead of just after '?'.

Previously it was able to match 'I' anywhere in the filenames of the svn info results instead of just files that where ignored or unknown to svn. This would cause 'make update' to infinitely recurse if a file was modified with I anywhere in its name since svn info would return a Path pointing to the llvm root for those files.