doc: build: Recommend DYLD_FALLBACK_LIBRARY_PATH rather than DYLD_LIBRARY_PATH

Using DYLD_LIBRARY_PATH can prevent system libraries from being loaded,
while DYLD_FALLBACK_LIBRARY_PATH does not, making it a safer option.


git-svn-id: https://svn.apache.org/repos/asf/xerces/c/trunk@1797566 13f79535-47bb-0310-9956-ffa450edef68