Compilation failure on macOS 10.15 Catalina

[Zach Pearson]

I think that Apple has changed the way the Xcode command line tools arrange 
headers on the system e.g. they are no longer put into /usr/include but exist 
in 

/Library/Developer/CommandLineTools/usr/include/

Because of this Emacs cannot find libxml/tree.h during the compilation process. 

I’ve found that adding this directory to ac_x_header_dirs in configure, then 
re-running ./configure, the trying to compile allows the program to build (the 
compiler output notes some deprecations but they’re just warnings). Is this a 
patch that should be upstream? 

Thanks for any guidance/feedback. I’m not sure if this is a permanent change 
and Apple intended for it to be that way or not. 

Zach