Use PHP 7.x style PDO include check

The PDO extensions bundled with PHP moved to this style (well, they
don't include the legacy check; this mirrors how it was in 7.3)

Pushed to CI branch to see how it affects it.

Author: NattyNarwhal

config.m4

@@ -62,17 +62,22 @@ if test "$PHP_PDO_IBM" != "no"; then
     done
   fi
 
-  AC_MSG_CHECKING([for PDO includes])
-  if test -f $abs_srcdir/include/php/ext/pdo/php_pdo_driver.h; then
-    pdo_inc_path=$abs_srcdir/ext
-  elif test -f $abs_srcdir/ext/pdo/php_pdo_driver.h; then
-    pdo_inc_path=$abs_srcdir/ext
-  elif test -f $prefix/include/php/ext/pdo/php_pdo_driver.h; then
-    pdo_inc_path=$prefix/include/php/ext
-  else
-    AC_MSG_ERROR([Cannot find php_pdo_driver.h.])
-  fi
-  AC_MSG_RESULT($pdo_inc_path)
+  ifdef([PHP_CHECK_PDO_INCLUDES],
+  [
+    PHP_CHECK_PDO_INCLUDES
+  ],[
+    AC_MSG_CHECKING([for PDO includes])
+    if test -f $abs_srcdir/include/php/ext/pdo/php_pdo_driver.h; then
+      pdo_cv_inc_path=$abs_srcdir/ext
+    elif test -f $abs_srcdir/ext/pdo/php_pdo_driver.h; then
+      pdo_cv_inc_path=$abs_srcdir/ext
+    elif test -f $phpincludedir/ext/pdo/php_pdo_driver.h; then
+      pdo_cv_inc_path=$phpincludedir/ext
+    else
+      AC_MSG_ERROR([Cannot find php_pdo_driver.h.])
+    fi
+    AC_MSG_RESULT($pdo_cv_inc_path)
+  ])
 
   dnl Don't forget to add additional source files here
   php_pdo_ibm_sources_core="pdo_ibm.c ibm_driver.c ibm_statement.c"