Need help building Emacs

[Xue Fuqiao]

Hi,

I'm not sure if this kind of post is considered on-topic on
emacs-devel.  If not, I can move it elsewhere (help-gnu-emacs,
perhaps?).

I just tried to build the latest emacs-25 branch on OS X 10.11.1, but failed:

   $ make install
[...]
     CC       xml.o
   xml.c:23:10: fatal error: 'libxml/tree.h' file not found
   #include <libxml/tree.h>
            ^
   1 error generated.
   make[1]: *** [xml.o] Error 1
   make: *** [src] Error 2

Among the output of my `./configure':

   [...]
   checking for LIBXML2... yes
   checking for htmlReadMemory in -lxml2... yes
   [...]
   Does Emacs use -lxml2?                                  yes
   [...]

IIRC OS X already provides libxml2, so I don't need to install one.  But
it seems that `make' cannot find `libxml/tree.h' in my header search
path.  Can anyone point me in the right direction?  How to troubleshoot
this kind of problem?

TIA