Autotools: Add phpized configure log and help separators (#15251)

- This quotes all PHP_CONFIGURE_PART arguments
- When configuring and building extensions with phpize, this makes the
  './configure --help' and './configure' log output a bit more readable
  as it separates the extension configuration, Libtool configuration and
  the rest of the Autoconf and phpize configuration options.
- The ./configure output separators bold tags are moved to the
  PHP_INIT_BUILD_SYSTEM macro to be available also in phpized extensions
- The obsolete ticks `...` converted to the recommended $(...); Autoconf
  configure re-executes itself in shells where the $(...) still wouldn't
  work ok. For example, the default, initial, non-updated shell on
  Solaris 10.
- Empty new lines in help separators synced (Autoconf default separators
  don't include additional empty newline after the separator title);
  so the PHP_HELP_SEPARATOR additional empty line is also removed
  (see './configure --help' output)

scripts/phpize.m4

@@ -139,11 +139,17 @@ PHP_BUILD_SHARED
 dnl Required programs.
 PHP_PROG_AWK
 
+PHP_HELP_SEPARATOR([Extension:])
+PHP_CONFIGURE_PART([Configuring extension])
+
 sinclude(config.m4)
 
 enable_static=no
 enable_shared=yes
 
+PHP_HELP_SEPARATOR([Libtool:])
+PHP_CONFIGURE_PART([Configuring libtool])
+
 dnl Only allow AC_PROG_CXX and AC_PROG_CXXCPP if they are explicitly called (by
 dnl PHP_REQUIRE_CXX). Otherwise AC_PROG_LIBTOOL fails if there is no working C++
 dnl compiler.
@@ -197,6 +203,8 @@ PHP_SUBST([SHELL])
 PHP_SUBST([INSTALL_HEADERS])
 PHP_SUBST([BUILD_CC])
 
+PHP_CONFIGURE_PART([Generating files])
+
 AC_CONFIG_HEADERS([config.h])
 
 AC_CONFIG_COMMANDS_PRE([PHP_PATCH_CONFIG_HEADERS([config.h.in])])