Ports: Add GNU Multiple Precision Arithmetic Library (GMP)

Author: https://github.com/bcoles
Commit: https://github.com/SerenityOS/serenity/commit/6c3e0cc98a2
Pull-request: https://github.com/SerenityOS/serenity/pull/6190

Ports/AvailablePorts.md

@@ -30,6 +30,7 @@ Please make sure to keep this list up to date when adding and updating ports. :^
 | [`gcc`](gcc/)                  | GNU Compiler Collection                       | 10.2.0            | https://gcc.gnu.org/                                  |
 | [`genemu`](genemu)             | Genesis / MegaDrive Emulator                  |                   | https://github.com/rasky/genemu                       |
 | [`git`](git/)                  | Git                                           | 2.26.0            | https://git-scm.com/                                  |
+| [`gmp`](gmp/)                  | GNU Multiple Precision Arithmetic Library     | 6.2.1             | https://gmplib.org/                                   |
 | [`gnuplot`](gnuplot/)          | Gnuplot                                       | 5.2.8             | http://www.gnuplot.info/                              |
 | [`grep`](grep/)                | GNU Grep                                      | 2.5.4             | https://www.gnu.org/software/grep/                    |
 | [`hatari`](hatari/)            | Atari ST/STE/TT/Falcon emulator               | 2.4.0-devel       | https://hatari.tuxfamily.org/                         |

Ports/gmp/package.sh

@@ -0,0 +1,9 @@
+#!/usr/bin/env -S bash ../.port_include.sh
+port=gmp
+version=6.2.1
+useconfigure="true"
+files="https://ftp.gnu.org/gnu/gmp/gmp-${version}.tar.bz2 gmp-${version}.tar.bz2
+https://ftp.gnu.org/gnu/gmp/gmp-${version}.tar.bz2.sig gmp-${version}.tar.bz2.sig
+https://ftp.gnu.org/gnu/gnu-keyring.gpg gnu-keyring.gpg"
+auth_type="sig"
+auth_opts="--keyring ./gnu-keyring.gpg gmp-${version}.tar.bz2.sig"

Ports/gmp/patches/configfsf.sub.patch

@@ -0,0 +1,10 @@
+--- gmp-6.2.1/configfsf.sub	2021-04-07 22:50:17.785886997 -0700
++++ gmp-6.2.1/configfsf.sub.new	2021-04-07 22:50:15.041883314 -0700
+@@ -1691,6 +1691,7 @@
+ 	# The portable systems comes first.
+ 	# Each alternative MUST end in a * to match a version number.
+ 	gnu* | android* | bsd* | mach* | minix* | genix* | ultrix* | irix* \
++	     | serenity* \
+ 	     | *vms* | esix* | aix* | cnk* | sunos | sunos[34]* \
+ 	     | hpux* | unos* | osf* | luna* | dgux* | auroraux* | solaris* \
+ 	     | sym* |  plan9* | psp* | sim* | xray* | os68k* | v88r* \