Remove warnings for bison and re2c checks

This patch removes warnings when lexer and parser files are already
generated. For example, when downloading a PHP release. Realistically,
it is not so trivial to rebuild lexer and parser files without removing
them first. And considering that tarballs don't have cleaning tools
such as Git, this would require manual removali.

Related also to https://bugs.gentoo.org/593278

Author: petk

build/php.m4

@@ -1838,9 +1838,7 @@ AC_DEFUN([PHP_PROG_BISON], [
 
   case $php_bison_check in
     ""|invalid[)]
-      if test -f "$abs_srcdir/Zend/zend_language_parser.h" && test -f "$abs_srcdir/Zend/zend_language_parser.c"; then
-        AC_MSG_WARN([bison $php_bison_required_version is required if you want to regenerate PHP parsers (excluded versions: $php_bison_excluded_versions)])
-      else
+      if test ! -f "$abs_srcdir/Zend/zend_language_parser.h" || test ! -f "$abs_srcdir/Zend/zend_language_parser.c"; then
         AC_MSG_ERROR([bison $php_bison_required_version is required to generate PHP parsers (excluded versions: $php_bison_excluded_versions).])
       fi
 
@@ -1895,9 +1893,7 @@ AC_DEFUN([PHP_PROG_RE2C],[
 
   case $php_re2c_check in
     ""|invalid[)]
-      if test -f "$abs_srcdir/Zend/zend_language_scanner.c"; then
-        AC_MSG_WARN([re2c $php_re2c_required_version is required if you want to regenerate PHP lexers.])
-      else
+      if test ! -f "$abs_srcdir/Zend/zend_language_scanner.c"; then
         AC_MSG_ERROR([re2c $php_re2c_required_version is required to generate PHP lexers.])
       fi