Use AC_SUBST for CONFIGURE_COMMAND and CONFIGURE_OPTIONS (#14445)

Instead of the PHP_SUBST_OLD, which also adds redundant variables to the
generated Makefile, these two can be done with AC_SUBST to be
substituted in the generated main/build-defs.h header and
scripts/php-config script.

Author: petk

build/php.m4

@@ -2029,8 +2029,8 @@ EOF
   echo '"[$]@"' >> $1
   chmod +x $1
   CONFIGURE_COMMAND="$CONFIGURE_COMMAND $CONFIGURE_OPTIONS"
-  PHP_SUBST_OLD(CONFIGURE_COMMAND)
-  PHP_SUBST_OLD(CONFIGURE_OPTIONS)
+  AC_SUBST([CONFIGURE_COMMAND])
+  AC_SUBST([CONFIGURE_OPTIONS])
 ])
 
 dnl