Description:
------------
THere is a build failure if you try and build a statically linked binary with 
both mbstring & libpng where png has a custom library dir.

This is because the png library has a header file config.h, and mbstring creates 
a header file config.h. During the build, the include path for libpng is 
included before the include path for the config generated mbstring path, so that 
when files inside mbstring try to #include "config.h" the first config.h 
discovered in the search patch is the one for png, not the one for mbstring.

e.g. the include path looks like

-I/home/foo/png_headers/include -I/home/foo/php/ext/mbstring/oniguruma -
I/home/foo/build/x86_64/ext/mbstring/oniguruma

Probably need to rename the config.h generated for mbstring by the configure 
script to something a little less likely to have conflicts.


Test script:
---------------
./configure --enable-embed=static --enable-mbstring --with-gd --with-png-dir=/some/custom/path
make all

Expected result:
----------------
Should build and link correctly.

Actual result:
--------------
ext/mbstring/oniguruma/regparse.c: In function ‘onig_scan_unsigned_number’:
ext/mbstring/oniguruma/regparse.c:1567: error: ‘SIZEOF_INT’ undeclared (first use 
in this function)
ext/mbstring/oniguruma/regparse.c:1567: error: (Each undeclared identifier is 
reported only once
ext/mbstring/oniguruma/regparse.c:1567: error: for each function it appears in.)
ext/mbstring/oniguruma/regparse.c: In function ‘scan_unsigned_hexadecimal_number’:
ext/mbstring/oniguruma/regparse.c:1595: error: ‘SIZEOF_INT’ undeclared (first use 
in this function)
ext/mbstring/oniguruma/regparse.c: In function ‘scan_unsigned_octal_number’:
ext/mbstring/oniguruma/regparse.c:1623: error: ‘SIZEOF_INT’ undeclared (first use 
in this function)