php: fix emalloc/efree/estrdup/... undefined references

zend_alloc.h defines some macros such as:

Where _estrdup is the actual function implemented by the PHP core. If
this header file is not included, and some code uses estrdup, one ends
up with an undefined reference. This happens when libexpat support is
enabled. This commit adds a PHP patch that fixes this issue. The patch
has been submitted upstream through a Github pull request.

Fixes:

  http://autobuild.buildroot.net/results/889d2c1f509c035cd506e36061939bfddc8f1500/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>