Ports: Add libfftw3

This is just the double-precision version of the already ported library.

Ports/AvailablePorts.md

@@ -142,6 +142,7 @@ This list is also available at [ports.serenityos.net](https://ports.serenityos.n
 | [`libenet`](libenet/)                               | libenet                                                         | 1.3.17                    | http://sauerbraten.org/enet/                                                   |
 | [`libexpat`](libexpat/)                             | Expat                                                           | 2.4.8                     | https://libexpat.github.io/                                                    |
 | [`libffi`](libffi/)                                 | libffi                                                          | 3.4.2                     | https://www.sourceware.org/libffi/                                             |
+| [`libfftw3`](libfftw3/)                             | Fastest Fourier Transform in the West (double precision)        | 3.3.10                    | https://www.fftw.org/                                                          |
 | [`libfftw3f`](libfftw3f/)                           | Fastest Fourier Transform in the West (single precision)        | 3.3.10                    | https://www.fftw.org/                                                          |
 | [`libfts`](libfts/)                                 | libfts                                                          | 1.2.7                     | https://github.com/void-linux/musl-fts                                         |
 | [`libgcrypt`](libgcrypt/)                           | libgcrypt                                                       | 1.10.1                    | https://gnupg.org/software/libgcrypt/index.html                                |

Ports/libfftw3/package.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env -S bash ../.port_include.sh
+port='libfftw3'
+version='3.3.10'
+useconfigure='true'
+use_fresh_config_sub='true'
+configopts=(
+    '--disable-static'
+    '--enable-shared'
+    '--with-pic'
+)
+files=(
+    "http://fftw.org/fftw-${version}.tar.gz#56c932549852cddcfafdab3820b0200c7742675be92179e59e6215b340e26467"
+)
+workdir="fftw-${version}"

Ports/libfftw3/patches/0001-libtool-Enable-shared-library-support-for-SerenityOS.patch

@@ -0,0 +1,73 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: =?UTF-8?q?kleines=20Filmr=C3=B6llchen?= <filmroellchen@serenityos.org>
+Date: Mon, 2 Oct 2023 16:56:18 +0200
+Subject: [PATCH] libtool: Enable shared library support for SerenityOS
+
+For some odd reason, libtool handles the configuration for shared
+libraries entirely statically and in its configure script. If no
+shared library support is "present", building shared libraries is
+disabled entirely.
+
+Fix that by just adding the appropriate configuration options for
+`serenity`. This allows us to finally create dynamic libraries
+automatically using libtool, without having to manually link the
+static library into a shared library.
+---
+ configure | 23 +++++++++++++++++++++++
+ 1 file changed, 23 insertions(+)
+
+diff --git a/configure b/configure
+index b59f977f59d1bfe5abe28a2e82ae500eb1bdfc60..f6bea050a946e7642ae907c7d50a1f2653434868 100755
+--- a/configure
++++ b/configure
+@@ -7140,6 +7140,10 @@ tpf*)
+ os2*)
+   lt_cv_deplibs_check_method=pass_all
+   ;;
++
++serenity*)
++  lt_cv_deplibs_check_method=pass_all
++  ;;
+ esac
+ 
+ fi
+@@ -10393,6 +10397,10 @@ lt_prog_compiler_static=
+       lt_prog_compiler_static='-Bstatic'
+       ;;
+ 
++    serenity*)
++      lt_prog_compiler_can_build_shared=yes
++      ;;
++
+     *)
+       lt_prog_compiler_can_build_shared=no
+       ;;
+@@ -11915,6 +11923,10 @@ $as_echo "$lt_cv_irix_exported_symbol" >&6; }
+       hardcode_shlibpath_var=no
+       ;;
+ 
++    serenity*)
++      ld_shlibs=yes
++      ;;
++
+     *)
+       ld_shlibs=no
+       ;;
+@@ -12995,6 +13007,17 @@ uts4*)
+   shlibpath_var=LD_LIBRARY_PATH
+   ;;
+ 
++serenity*)
++  version_type=linux
++  need_lib_prefix=no
++  need_version=no
++  library_names_spec='${libname}${release}${shared_ext}${versuffix} ${libname}${release}${shared_ext}${major} ${libname}${shared_ext}'
++  soname_spec='${libname}${release}${shared_ext}${major}'
++  shlibpath_var=LD_LIBRARY_PATH
++  shlibpath_overrides_runpath=no
++  dynamic_linker='SerenityOS LibELF'
++  ;;
++
+ *)
+   dynamic_linker=no
+   ;;

Ports/libfftw3/patches/ReadMe.md

@@ -0,0 +1,16 @@
+# Patches for libfftw3 on SerenityOS
+
+## `0001-libtool-Enable-shared-library-support-for-SerenityOS.patch`
+
+libtool: Enable shared library support for SerenityOS
+
+For some odd reason, libtool handles the configuration for shared
+libraries entirely statically and in its configure script. If no
+shared library support is "present", building shared libraries is
+disabled entirely.
+
+Fix that by just adding the appropriate configuration options for
+`serenity`. This allows us to finally create dynamic libraries
+automatically using libtool, without having to manually link the
+static library into a shared library.
+