php.extensions.readline: Actually use readline

Building readline extension would say:

    checking for libedit readline replacement... yes, shared

even when configuring `--without-libedit`. This is because `PHP_ARG_WITH(libedit, …)`, internally calls `PHP_ALWAYS_SHARED`, which in `phpize`-generated `configure.ac` is defined as always forcing the value to shared. This will prevent `PHP_ARG_WITH(readline, …)` from being invoked so `READLINE_DIR` variable will never be defined.

This was not an issue before we split the extension out of php.unwrapped in 282337799b, as `PHP_ALWAYS_SHARED` is empty there.

-----

Additionally, because the build script passed `-L$READLINE_DIR/lib` as a flag to the compiler on PHP < 7.4 (built by the nix-phps repository), this ended up with a FHS-like path being passed to the linker. And once we bumped GCC to 11 in 52f8cf58a4, the linker would fail:

	  gcc -shared  .libs/readline.o .libs/readline_cli.o  -Wl,--rpath -Wl,/lib -L/lib -ledit -lncurses  -Wl,-soname -Wl,readline.so -o .libs/readline.so
	  impure path `/lib' used in link
	  collect2: error: ld returned 1 exit status

This no longer happens with PHP ≥ 7.4, since they switched to getting the linker flags from pkg-config in b537203d20.

----

As a compromise, let’s make the `PHP_ALWAYS_SHARED` function force `shared` status but only for flags that are not disabled. That will allow us to remove the libedit dependency and also the nasty patch for configure script due to `--with-libedit` not being passed (which would be required for PHP < 7.4 to be able to find readline.h from libedit).

Thanks to Pol Dellaiera for both bisections.

pkgs/top-level/php-packages.nix

@@ -19,7 +19,6 @@
 , html-tidy
 , icu64
 , libXpm
-, libedit
 , libffi
 , libiconv
 , libjpeg
@@ -542,10 +541,23 @@ lib.makeScope pkgs.newScope (self: with self; {
         { name = "pspell"; configureFlags = [ "--with-pspell=${aspell}" ]; }
         {
           name = "readline";
-          buildInputs = [ libedit readline ];
-          configureFlags = [ "--with-readline=${readline.dev}" ];
-          postPhpize = lib.optionalString (lib.versionOlder php.version "7.4") ''
-            substituteInPlace configure --replace 'as_fn_error $? "Please reinstall libedit - I cannot find readline.h" "$LINENO" 5' ':'
+          buildInputs = [
+            readline
+          ];
+          configureFlags = [
+            "--with-readline=${readline.dev}"
+          ];
+          postPatch = ''
+            # Fix `--with-readline` option not being available.
+            # `PHP_ALWAYS_SHARED` generated by phpize enables all options
+            # without the possibility to override them. But when `--with-libedit`
+            # is enabled, `--with-readline` is not registered.
+            echo '
+            AC_DEFUN([PHP_ALWAYS_SHARED],[
+              test "[$]$1" != "no" && ext_shared=yes
+            ])dnl
+            ' | cat - ext/readline/config.m4 > ext/readline/config.m4.tmp
+            mv ext/readline/config.m4{.tmp,}
           '';
           doCheck = false;
         }